$AVA
AVISTA CORP Stock $ava

$ava Overview Financials Valuation SEC Filings Company Website

2017 Form 10-K Financial Statement

#000010491818000043 Filed on February 21, 2018

Income Statement

Concept	2017	2016 Q4	2016 Q3
Revenue	$1.446B	$402.1M	$303.3M
YoY Change	0.24%	3.83%	-3.28%
Cost Of Revenue
YoY Change
Gross Profit
YoY Change
Gross Profit Margin
Selling, General & Admin
YoY Change
% of Gross Profit
Research & Development
YoY Change
% of Gross Profit
Depreciation & Amortization	$175.7M	$42.50M	$41.30M
YoY Change	6.51%	10.97%	10.43%
% of Gross Profit
Operating Expenses	$1.139B	$309.5M	$263.8M
YoY Change	-0.3%	-2.34%	-5.01%
Operating Profit	$292.2M	$82.53M	$39.59M
YoY Change	-2.56%	17.29%	10.25%
Interest Expense	$95.36M	-$22.10M	$21.63M
YoY Change	10.25%	11.62%	8.43%
% of Operating Profit	32.64%	-26.78%	54.63%
Other Income/Expense, Net	-$607.0K	-$7.000M	$1.562M
YoY Change	-3135.0%	-305.88%	-26.42%
Pretax Income	$198.7M	$63.50M	$19.87M
YoY Change	-7.76%	17.81%	5.29%
Income Tax	$82.76M	$23.40M	$7.606M
% Of Pretax Income	41.65%	36.85%	38.28%
Net Earnings	$115.9M	$40.09M	$12.23M
YoY Change	-15.53%	4.08%	-5.97%
Net Earnings / Revenue	8.02%	9.97%	4.03%
Basic Earnings Per Share	$1.80		$0.19
Diluted Earnings Per Share	$1.79	$0.62	$0.19
COMMON SHARES
Basic Shares Outstanding	64.50M shares	64.19M shares	63.86M shares
Diluted Shares Outstanding	64.81M shares	64.62M shares	64.33M shares

Balance Sheet

Concept	2017	2016 Q4	2016 Q3
SHORT-TERM ASSETS
Cash & Short-Term Investments	$16.00M	$9.000M	$7.000M
YoY Change	77.78%	-10.0%	-22.22%
Cash & Equivalents	$16.00M	$8.507M	$7.084M
Short-Term Investments
Other Short-Term Assets	$77.00M	$49.63M	$35.88M
YoY Change	26.23%	62.07%	-8.19%
Inventory	$58.00M	$53.31M	$58.08M
Prepaid Expenses
Receivables	$186.0M	$180.0M	$116.0M
Other Receivables	$0.00	$49.00M	$49.00M
Total Short-Term Assets	$338.0M	$351.3M	$284.4M
YoY Change	-3.7%	14.8%	10.23%
LONG-TERM ASSETS
Property, Plant & Equipment	$4.399B	$4.147B	$4.057B
YoY Change	6.08%	6.36%	7.21%
Goodwill		$57.67M	$57.67M
YoY Change		0.0%	0.0%
Intangibles
YoY Change
Long-Term Investments	$93.00M	$84.00M	$74.00M
YoY Change	10.71%	18.31%	13.85%
Other Assets	$628.0M	$141.4M	$136.0M
YoY Change	-6.13%	-1.53%	-3.29%
Total Long-Term Assets	$5.177B	$4.958B	$4.931B
YoY Change	4.4%	7.78%	10.03%
TOTAL ASSETS
Total Short-Term Assets	$338.0M	$351.3M	$284.4M
Total Long-Term Assets	$5.177B	$4.958B	$4.931B
Total Assets	$5.515B	$5.310B	$5.215B
YoY Change	3.86%	8.22%	10.04%
SHORT-TERM LIABILITIES
YoY Change
Accounts Payable	$107.0M	$115.5M	$81.90M
YoY Change	-7.76%	1.05%	29.64%
Accrued Expenses	$50.00M	$49.00M
YoY Change	2.04%
Deferred Revenue
YoY Change
Short-Term Debt	$105.0M	$120.0M	$84.00M
YoY Change	-12.5%	14.29%	-35.38%
Long-Term Debt Due	$277.0M	$3.000M	$3.000M
YoY Change	9133.33%	-96.77%	-96.77%
Total Short-Term Liabilities	$698.0M	$407.5M	$341.9M
YoY Change	71.08%	-14.15%	-23.64%
LONG-TERM LIABILITIES
Long-Term Debt	$1.543B	$1.730B	$1.730B
YoY Change	-10.81%	12.92%	19.89%
Other Long-Term Liabilities	$1.077B	$153.3M	$135.6M
YoY Change	57.69%	17.2%	-18.25%
Total Long-Term Liabilities	$2.620B	$153.3M	$135.6M
YoY Change	8.58%	17.2%	-18.25%
TOTAL LIABILITIES
Total Short-Term Liabilities	$698.0M	$407.5M	$341.9M
Total Long-Term Liabilities	$2.620B	$153.3M	$135.6M
Total Liabilities	$3.785B	$3.661B	$3.587B
YoY Change	3.39%	8.37%	11.01%
SHAREHOLDERS EQUITY
Retained Earnings		$581.0M	$562.9M
YoY Change		9.43%	9.73%
Common Stock		$1.075B	$1.073B
YoY Change		7.06%	7.06%
Preferred Stock
YoY Change
Treasury Stock (at cost)
YoY Change
Treasury Stock Shares
Shareholders Equity	$1.730B	$1.649B	$1.629B
YoY Change
Total Liabilities & Shareholders Equity	$5.515B	$5.310B	$5.215B
YoY Change	3.86%	8.22%	10.04%

Cashflow Statement

Concept	2017	2016 Q4	2016 Q3
OPERATING ACTIVITIES
Net Income	$115.9M	$40.09M	$12.23M
YoY Change	-15.53%	4.08%	-5.97%
Depreciation, Depletion And Amortization	$175.7M	$42.50M	$41.30M
YoY Change	6.51%	10.97%	10.43%
Cash From Operating Activities	$410.3M	$104.2M	$98.10M
YoY Change	14.52%	61.8%	24.02%
INVESTING ACTIVITIES
Capital Expenditures	$412.3M	-$118.7M	-$105.3M
YoY Change	1.4%	-1.58%	10.38%
Acquisitions
YoY Change
Other Investing Activities	$4.384M	$1.100M	-$3.000M
YoY Change	-42.55%	-71.79%	2900.0%
Cash From Investing Activities	-$434.1M	-$117.5M	-$108.4M
YoY Change	0.38%	0.69%	13.51%
FINANCING ACTIVITIES
Cash Dividend Paid	$92.46M
YoY Change	6.09%
Common Stock Issuance & Retirement, Net	-$56.38M
YoY Change	-15.79%
Debt Paid & Issued, Net	$3.287M
YoY Change	-97.99%
Cash From Financing Activities	$31.47M	14.80M	3.700M
YoY Change	-56.43%	-72.34%	-60.64%
NET CHANGE
Cash From Operating Activities	$410.3M	104.2M	98.10M
Cash From Investing Activities	-$434.1M	-117.5M	-108.4M
Cash From Financing Activities	$31.47M	14.80M	3.700M
Net Change In Cash	$7.665M	1.500M	-6.600M
YoY Change	-487.71%	25.0%	-5.71%
FREE CASH FLOW
Cash From Operating Activities	$410.3M	$104.2M	$98.10M
Capital Expenditures	$412.3M	-$118.7M	-$105.3M
Free Cash Flow	-$2.041M	$222.9M	$203.4M
YoY Change	-95.78%	20.49%	16.56%

Facts In Submission

Frame	Concept Type	Concept / XBRL Key	Value	Unit
CY2017Q4	ava	Accumulated Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Net Unamortized Gain Loss Tax AccumulatedOtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossTax	4356000	USD
CY2015	ava	Amortization Of Energy Contract AmortizationOfEnergyContract	13508000	USD
CY2016	ava	Amortization Of Energy Contract AmortizationOfEnergyContract	14694000	USD
CY2017	ava	Amortization Of Energy Contract AmortizationOfEnergyContract	0	USD
CY2017Q4	ava	Amount Available For Dividend Distribution Without Affecting Covenants AmountAvailableForDividendDistributionWithoutAffectingCovenants	97600000	USD
CY2016	ava	Company Shareof Benefit Expense Under Washington Energy Recovery Mechanism CompanyShareofBenefitExpenseUnderWashingtonEnergyRecoveryMechanism	5100000	USD
CY2017	ava	Company Shareof Benefit Expense Under Washington Energy Recovery Mechanism CompanyShareofBenefitExpenseUnderWashingtonEnergyRecoveryMechanism	4600000	USD
CY2016Q4	ava	Current Regulatory Asset For Utility Derivatives CurrentRegulatoryAssetForUtilityDerivatives	11365000	USD
CY2017Q4	ava	Current Regulatory Asset For Utility Derivatives CurrentRegulatoryAssetForUtilityDerivatives	24991000	USD
CY2016Q4	ava	Deferred Income Tax Assets Power And Natural Gas Deferrals DeferredIncomeTaxAssetsPowerAndNaturalGasDeferrals	19415000	USD
CY2016Q4	ava	Accumulated Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Net Unamortized Gain Loss Tax AccumulatedOtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossTax	4075000	USD
CY2017Q4	ava	Deferred Income Tax Assets Power And Natural Gas Deferrals DeferredIncomeTaxAssetsPowerAndNaturalGasDeferrals	14379000	USD
CY2015	ava	Deferred Income Tax Expense Benefit Continuing Operationsand Discontinued Operations DeferredIncomeTaxExpenseBenefitContinuingOperationsandDiscontinuedOperations	51801000	USD
CY2016	ava	Deferred Income Tax Expense Benefit Continuing Operationsand Discontinued Operations DeferredIncomeTaxExpenseBenefitContinuingOperationsandDiscontinuedOperations	124543000	USD
CY2017	ava	Deferred Income Tax Expense Benefit Continuing Operationsand Discontinued Operations DeferredIncomeTaxExpenseBenefitContinuingOperationsandDiscontinuedOperations	69657000	USD
CY2016Q4	ava	Deferred Tax Assets Regulatory Deferred Tax Credits DeferredTaxAssetsRegulatoryDeferredTaxCredits	15192000	USD
CY2017Q4	ava	Deferred Tax Assets Regulatory Deferred Tax Credits DeferredTaxAssetsRegulatoryDeferredTaxCredits	6359000	USD
CY2016Q4	ava	Deferred Tax Liabilities Loss On Reacquired Debt DeferredTaxLiabilitiesLossOnReacquiredDebt	31955000	USD
CY2017Q4	ava	Deferred Tax Liabilities Loss On Reacquired Debt DeferredTaxLiabilitiesLossOnReacquiredDebt	19992000	USD
CY2016Q4	ava	Deferred Tax Liabilities Settlement With Specific External Party DeferredTaxLiabilitiesSettlementWithSpecificExternalParty	11711000	USD
CY2017Q4	ava	Deferred Tax Liabilities Settlement With Specific External Party DeferredTaxLiabilitiesSettlementWithSpecificExternalParty	6802000	USD
CY2016Q4	ava	Deferred Tax Liabilityfor Regulatory Asseton Pensionand Other Postretirement Benefits DeferredTaxLiabilityforRegulatoryAssetonPensionandOtherPostretirementBenefits	84040000	USD
CY2017Q4	ava	Deferred Tax Liabilityfor Regulatory Asseton Pensionand Other Postretirement Benefits DeferredTaxLiabilityforRegulatoryAssetonPensionandOtherPostretirementBenefits	43914000	USD
CY2016Q4	ava	Deferredtaxliabilityforregulatoryassetonutilitypropertyplantandequipment Deferredtaxliabilityforregulatoryassetonutilitypropertyplantandequipment	37301000	USD
CY2017Q4	ava	Deferredtaxliabilityforregulatoryassetonutilitypropertyplantandequipment Deferredtaxliabilityforregulatoryassetonutilitypropertyplantandequipment	81860000	USD
CY2015	ava	Depreciation And Amortization Expense DepreciationAndAmortizationExpense	144194000	USD
CY2016	ava	Depreciation And Amortization Expense DepreciationAndAmortizationExpense	161283000	USD
CY2017	ava	Depreciation And Amortization Expense DepreciationAndAmortizationExpense	172021000	USD
CY2015	ava	Discontinued Operation Gain Loss From Disposal Of Discontinued Operation Before Income Taxes Netof Transaction Costs DiscontinuedOperationGainLossFromDisposalOfDiscontinuedOperationBeforeIncomeTaxesNetofTransactionCosts	706000	USD
CY2015	ava	Income Tax Reconciliation Nondeductible Expense Acquisition Costs Amount IncomeTaxReconciliationNondeductibleExpenseAcquisitionCostsAmount	0	USD
CY2016	ava	Income Tax Reconciliation Nondeductible Expense Acquisition Costs Amount IncomeTaxReconciliationNondeductibleExpenseAcquisitionCostsAmount	0	USD
CY2017	ava	Income Tax Reconciliation Nondeductible Expense Acquisition Costs Amount IncomeTaxReconciliationNondeductibleExpenseAcquisitionCostsAmount	2491000	USD
CY2015	ava	Income Tax Reconciliation Nondeductible Expense Acquisition Costs Percent IncomeTaxReconciliationNondeductibleExpenseAcquisitionCostsPercent	0.000
CY2016	ava	Income Tax Reconciliation Nondeductible Expense Acquisition Costs Percent IncomeTaxReconciliationNondeductibleExpenseAcquisitionCostsPercent	0.000
CY2017	ava	Income Tax Reconciliation Nondeductible Expense Acquisition Costs Percent IncomeTaxReconciliationNondeductibleExpenseAcquisitionCostsPercent	0.013
CY2015	ava	Income Tax Reconciliation Settlementof Share Based Compensation Amount IncomeTaxReconciliationSettlementofShareBasedCompensationAmount	0	USD
CY2016	ava	Income Tax Reconciliation Settlementof Share Based Compensation Amount IncomeTaxReconciliationSettlementofShareBasedCompensationAmount	1597000	USD
CY2017	ava	Income Tax Reconciliation Settlementof Share Based Compensation Amount IncomeTaxReconciliationSettlementofShareBasedCompensationAmount	1439000	USD
CY2015	ava	Income Tax Reconciliation Settlementof Share Based Compensation Percent IncomeTaxReconciliationSettlementofShareBasedCompensationPercent	0.000
CY2016	ava	Income Tax Reconciliation Settlementof Share Based Compensation Percent IncomeTaxReconciliationSettlementofShareBasedCompensationPercent	0.007
CY2017	ava	Income Tax Reconciliation Settlementof Share Based Compensation Percent IncomeTaxReconciliationSettlementofShareBasedCompensationPercent	0.007
CY2015	ava	Increase Decrease In Regulatory Assets And Liabilities Associatedwith Alternative Revenue Programs IncreaseDecreaseInRegulatoryAssetsAndLiabilitiesAssociatedwithAlternativeRevenuePrograms	10933000	USD
CY2016	ava	Increase Decrease In Regulatory Assets And Liabilities Associatedwith Alternative Revenue Programs IncreaseDecreaseInRegulatoryAssetsAndLiabilitiesAssociatedwithAlternativeRevenuePrograms	29789000	USD
CY2017	ava	Increase Decrease In Regulatory Assets And Liabilities Associatedwith Alternative Revenue Programs IncreaseDecreaseInRegulatoryAssetsAndLiabilitiesAssociatedwithAlternativeRevenuePrograms	-24179000	USD
CY2015	ava	Interest Expense Including Affiliated Trusts InterestExpenseIncludingAffiliatedTrusts	80441000	USD
CY2016	ava	Interest Expense Including Affiliated Trusts InterestExpenseIncludingAffiliatedTrusts	87130000	USD
CY2017	ava	Interest Expense Including Affiliated Trusts InterestExpenseIncludingAffiliatedTrusts	96192000	USD
CY2015	ava	Interest On Regulatory Deferrals InterestOnRegulatoryDeferrals	48000	USD
CY2016	ava	Interest On Regulatory Deferrals InterestOnRegulatoryDeferrals	1308000	USD
CY2017	ava	Interest On Regulatory Deferrals InterestOnRegulatoryDeferrals	1288000	USD
CY2016Q4	ava	Long Term Debt Before Current Portion And Bonds Held By Company LongTermDebtBeforeCurrentPortionAndBondsHeldByCompany	1765704000	USD
CY2017Q4	ava	Long Term Debt Before Current Portion And Bonds Held By Company LongTermDebtBeforeCurrentPortionAndBondsHeldByCompany	1852937000	USD
CY2017Q4	ava	Maximum Dividend Increase Allowed Per Merger Agreement MaximumDividendIncreaseAllowedPerMergerAgreement	0.06	USD
CY2016Q4	ava	Noncurrent Regulatory Asset For Utility Derivatives NoncurrentRegulatoryAssetForUtilityDerivatives	16919000	USD
CY2017Q4	ava	Noncurrent Regulatory Asset For Utility Derivatives NoncurrentRegulatoryAssetForUtilityDerivatives	18967000	USD
CY2017	ava	Number Of Days Canadian Currency Prices Are Settled With Us Dollars NumberOfDaysCanadianCurrencyPricesAreSettledWithUSDollars	P60D
CY2015	ava	Other Operating Expenses OtherOperatingExpenses	332747000	USD
CY2016	ava	Other Operating Expenses OtherOperatingExpenses	341296000	USD
CY2017	ava	Other Operating Expenses OtherOperatingExpenses	358081000	USD
CY2015	ava	Paymentsfor Settlementof Derivative Instruments Operating Activities PaymentsforSettlementofDerivativeInstrumentsOperatingActivities	0	USD
CY2016	ava	Paymentsfor Settlementof Derivative Instruments Operating Activities PaymentsforSettlementofDerivativeInstrumentsOperatingActivities	53966000	USD
CY2017	ava	Paymentsfor Settlementof Derivative Instruments Operating Activities PaymentsforSettlementofDerivativeInstrumentsOperatingActivities	11302000	USD
CY2017Q3	ava	Paymentsforproceedsfromderivativeinstrumentoperatingactivities Paymentsforproceedsfromderivativeinstrumentoperatingactivities	8800000	USD
CY2017Q4	ava	Pending Regulatory Treatment Liability PendingRegulatoryTreatmentLiability	453120000	USD
CY2017Q4	ava	Percentof Interest Rate Swaps Allocatedto Washington PercentofInterestRateSwapsAllocatedtoWashington	0.60
CY2015	ava	Proceedsfrom Settlementof Derivative Instruments ProceedsfromSettlementofDerivativeInstruments	0	USD
CY2016	ava	Proceedsfrom Settlementof Derivative Instruments ProceedsfromSettlementofDerivativeInstruments	0	USD
CY2017	ava	Proceedsfrom Settlementof Derivative Instruments ProceedsfromSettlementofDerivativeInstruments	2479000	USD
CY2016Q4	ava	Property Plant And Equipment Total PropertyPlantAndEquipmentTotal	5687737000	USD
CY2017Q4	ava	Property Plant And Equipment Total PropertyPlantAndEquipmentTotal	6047930000	USD
CY2015	ava	Public Utility Operating Expenses Excise Taxes Collected PublicUtilityOperatingExpensesExciseTaxesCollected	59173000	USD
CY2016	ava	Public Utility Operating Expenses Excise Taxes Collected PublicUtilityOperatingExpensesExciseTaxesCollected	57745000	USD
CY2017	ava	Public Utility Operating Expenses Excise Taxes Collected PublicUtilityOperatingExpensesExciseTaxesCollected	64012000	USD
CY2015	ava	Public Utility Operating Expenses Other Taxes PublicUtilityOperatingExpensesOtherTaxes	2536000	USD
CY2016	ava	Public Utility Operating Expenses Other Taxes PublicUtilityOperatingExpensesOtherTaxes	2485000	USD
CY2017	ava	Public Utility Operating Expenses Other Taxes PublicUtilityOperatingExpensesOtherTaxes	2666000	USD
CY2017Q4	ava	Regulatory Asset Earning Return RegulatoryAssetEarningReturn	258930000	USD
CY2016Q4	ava	Regulatory Asset For Interest Rate Swap Agreements Noncurrent RegulatoryAssetForInterestRateSwapAgreementsNoncurrent	161508000	USD
CY2017Q4	ava	Regulatory Asset For Interest Rate Swap Agreements Noncurrent RegulatoryAssetForInterestRateSwapAgreementsNoncurrent	169704000	USD
CY2016Q4	ava	Regulatory Assetfor Deferred Income Taxes Noncurrent RegulatoryAssetforDeferredIncomeTaxesNoncurrent	109853000	USD
CY2017Q4	ava	Regulatory Assetfor Deferred Income Taxes Noncurrent RegulatoryAssetforDeferredIncomeTaxesNoncurrent	90315000	USD
CY2016Q4	ava	Regulatory Assets For Pensions And Other Postretirement Benefits Noncurrent RegulatoryAssetsForPensionsAndOtherPostretirementBenefitsNoncurrent	240114000	USD
CY2017Q4	ava	Regulatory Assets For Pensions And Other Postretirement Benefits Noncurrent RegulatoryAssetsForPensionsAndOtherPostretirementBenefitsNoncurrent	209115000	USD
CY2017Q4	ava	Regulatory Liability Earning Return RegulatoryLiabilityEarningReturn	372132000	USD
CY2016Q4	ava	Regulatory Liability For Utility Plant Retirement Costs Noncurrent RegulatoryLiabilityForUtilityPlantRetirementCostsNoncurrent	273983000	USD
CY2017Q4	ava	Regulatory Liability For Utility Plant Retirement Costs Noncurrent RegulatoryLiabilityForUtilityPlantRetirementCostsNoncurrent	285786000	USD
CY2016Q4	ava	Regulatory Liabilityfor Excess Deferred Income Taxes RegulatoryLiabilityforExcessDeferredIncomeTaxes	0	USD
CY2017Q4	ava	Regulatory Liabilityfor Excess Deferred Income Taxes RegulatoryLiabilityforExcessDeferredIncomeTaxes	442319000	USD
CY2017Q4	ava	Remaining Amounts Of Regulatory Liabilities For Which No Interest During Recovery Period Is Provided RemainingAmountsOfRegulatoryLiabilitiesForWhichNoInterestDuringRecoveryPeriodIsProvided	23101000	USD
CY2016Q4	ava	Securedand Unsecured Debt SecuredandUnsecuredDebt	1711700000	USD
CY2017Q4	ava	Securedand Unsecured Debt SecuredandUnsecuredDebt	1801700000	USD
CY2017	ava	Tcja Changein Income Tax Expense Benefit TCJAChangeinIncomeTaxExpenseBenefit	10200000	USD
CY2017Q4	ava	Tax Cutsand Jobs Act Excess Deferred Income Taxes TaxCutsandJobsActExcessDeferredIncomeTaxes	339900000	USD
CY2017Q4	ava	Tax Cutsand Jobs Act Income Tax Gross Upof Excess Deferred Income Taxes TaxCutsandJobsActIncomeTaxGrossUpofExcessDeferredIncomeTaxes	102400000	USD
CY2015	ava	Tax Effect Of Regulatory Treatment Of Utility Plant Differences TaxEffectOfRegulatoryTreatmentOfUtilityPlantDifferences	4358000	USD
CY2016	ava	Tax Effect Of Regulatory Treatment Of Utility Plant Differences TaxEffectOfRegulatoryTreatmentOfUtilityPlantDifferences	3297000	USD
CY2017	ava	Tax Effect Of Regulatory Treatment Of Utility Plant Differences TaxEffectOfRegulatoryTreatmentOfUtilityPlantDifferences	3482000	USD
CY2015	ava	Tax Effect Of Regulatory Treatment Of Utility Plant Differences Percent TaxEffectOfRegulatoryTreatmentOfUtilityPlantDifferencesPercent	0.023
CY2016	ava	Tax Effect Of Regulatory Treatment Of Utility Plant Differences Percent TaxEffectOfRegulatoryTreatmentOfUtilityPlantDifferencesPercent	0.015
CY2017	ava	Tax Effect Of Regulatory Treatment Of Utility Plant Differences Percent TaxEffectOfRegulatoryTreatmentOfUtilityPlantDifferencesPercent	0.017
CY2015	ava	Utility Power Resources UtilityPowerResources	511937000	USD
CY2016	ava	Utility Power Resources UtilityPowerResources	402575000	USD
CY2017	ava	Utility Power Resources UtilityPowerResources	380523000	USD
CY2017	dei	Amendment Flag AmendmentFlag	false
CY2017	dei	Current Fiscal Year End Date CurrentFiscalYearEndDate	--12-31
CY2017	dei	Document Fiscal Period Focus DocumentFiscalPeriodFocus	FY
CY2017	dei	Document Fiscal Year Focus DocumentFiscalYearFocus	2017
CY2017	dei	Document Period End Date DocumentPeriodEndDate	2017-12-31
CY2017	dei	Document Type DocumentType	10-K
CY2017	dei	Entity Central Index Key EntityCentralIndexKey	0000104918
CY2018Q1	dei	Entity Common Stock Shares Outstanding EntityCommonStockSharesOutstanding	65628172	shares
CY2017	dei	Entity Current Reporting Status EntityCurrentReportingStatus	Yes
CY2017	dei	Entity Filer Category EntityFilerCategory	Large Accelerated Filer
CY2017Q2	dei	Entity Public Float EntityPublicFloat	2734805418	USD
CY2017	dei	Entity Registrant Name EntityRegistrantName	AVISTA CORP
CY2017	dei	Trading Symbol TradingSymbol	ava
CY2016Q4	us-gaap	Accounts Notes And Loans Receivable Net Current AccountsNotesAndLoansReceivableNetCurrent	180265000	USD
CY2017	dei	Entity Voluntary Filers EntityVoluntaryFilers	No
CY2017	dei	Entity Well Known Seasoned Issuer EntityWellKnownSeasonedIssuer	Yes
CY2017Q4	us-gaap	Accounts Notes And Loans Receivable Net Current AccountsNotesAndLoansReceivableNetCurrent	185664000	USD
CY2016Q4	us-gaap	Accounts Payable Current AccountsPayableCurrent	115545000	USD
CY2017Q4	us-gaap	Accounts Payable Current AccountsPayableCurrent	107289000	USD
CY2016Q4	us-gaap	Accrual For Taxes Other Than Income Taxes Current AccrualForTaxesOtherThanIncomeTaxesCurrent	33374000	USD
CY2017Q4	us-gaap	Accrual For Taxes Other Than Income Taxes Current AccrualForTaxesOtherThanIncomeTaxesCurrent	33802000	USD
CY2016Q4	us-gaap	Accumulated Other Comprehensive Income Loss Defined Benefit Pension And Other Postretirement Plans Net Of Tax AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax	-7568000	USD
CY2017Q4	us-gaap	Accumulated Other Comprehensive Income Loss Defined Benefit Pension And Other Postretirement Plans Net Of Tax AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax	-8090000	USD
CY2016Q4	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	-7568000	USD
CY2017Q4	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	-8090000	USD
CY2015	us-gaap	Allocated Share Based Compensation Expense AllocatedShareBasedCompensationExpense	6914000	USD
CY2016	us-gaap	Allocated Share Based Compensation Expense AllocatedShareBasedCompensationExpense	7891000	USD
CY2017	us-gaap	Allocated Share Based Compensation Expense AllocatedShareBasedCompensationExpense	7359000	USD
CY2014Q4	us-gaap	Allowance For Doubtful Accounts Receivable Current AllowanceForDoubtfulAccountsReceivableCurrent	4888000	USD
CY2015Q4	us-gaap	Allowance For Doubtful Accounts Receivable Current AllowanceForDoubtfulAccountsReceivableCurrent	4530000	USD
CY2016Q4	us-gaap	Allowance For Doubtful Accounts Receivable Current AllowanceForDoubtfulAccountsReceivableCurrent	5026000	USD
CY2017Q4	us-gaap	Allowance For Doubtful Accounts Receivable Current AllowanceForDoubtfulAccountsReceivableCurrent	5132000	USD
CY2015	us-gaap	Amortization Of Financing Costs AmortizationOfFinancingCosts	3526000	USD
CY2016	us-gaap	Amortization Of Financing Costs AmortizationOfFinancingCosts	3477000	USD
CY2017	us-gaap	Amortization Of Financing Costs AmortizationOfFinancingCosts	3254000	USD
CY2015	us-gaap	Amortization Of Power Contracts Emission Credits AmortizationOfPowerContractsEmissionCredits	2450000	USD
CY2016	us-gaap	Amortization Of Power Contracts Emission Credits AmortizationOfPowerContractsEmissionCredits	2450000	USD
CY2017	us-gaap	Amortization Of Power Contracts Emission Credits AmortizationOfPowerContractsEmissionCredits	2450000	USD
CY2017Q4	us-gaap	Amount Of Regulatory Costs Not Yet Approved AmountOfRegulatoryCostsNotYetApproved	120462000	USD
CY2014Q4	us-gaap	Asset Retirement Obligation AssetRetirementObligation	3028000	USD
CY2015Q4	us-gaap	Asset Retirement Obligation AssetRetirementObligation	15997000	USD
CY2016Q4	us-gaap	Asset Retirement Obligation AssetRetirementObligation	15515000	USD
CY2017Q4	us-gaap	Asset Retirement Obligation AssetRetirementObligation	17482000	USD
CY2015	us-gaap	Asset Retirement Obligation Accretion Expense AssetRetirementObligationAccretionExpense	459000	USD
CY2016	us-gaap	Asset Retirement Obligation Accretion Expense AssetRetirementObligationAccretionExpense	617000	USD
CY2017	us-gaap	Asset Retirement Obligation Accretion Expense AssetRetirementObligationAccretionExpense	796000	USD
CY2015	us-gaap	Asset Retirement Obligation Liabilities Incurred AssetRetirementObligationLiabilitiesIncurred	12539000	USD
CY2016	us-gaap	Asset Retirement Obligation Liabilities Incurred AssetRetirementObligationLiabilitiesIncurred	430000	USD
CY2017	us-gaap	Asset Retirement Obligation Liabilities Incurred AssetRetirementObligationLiabilitiesIncurred	1171000	USD
CY2015	us-gaap	Asset Retirement Obligation Liabilities Settled AssetRetirementObligationLiabilitiesSettled	29000	USD
CY2016	us-gaap	Asset Retirement Obligation Liabilities Settled AssetRetirementObligationLiabilitiesSettled	1529000	USD
CY2017	us-gaap	Asset Retirement Obligation Liabilities Settled AssetRetirementObligationLiabilitiesSettled	0	USD
CY2015Q4	us-gaap	Assets Assets	4906649000	USD
CY2016Q4	us-gaap	Assets Assets	5309755000	USD
CY2017Q4	us-gaap	Assets Assets	5514732000	USD
CY2016Q4	us-gaap	Assets Current AssetsCurrent	351341000	USD
CY2017Q4	us-gaap	Assets Current AssetsCurrent	337534000	USD
CY2015	us-gaap	Business Combination Acquisition Related Costs BusinessCombinationAcquisitionRelatedCosts	0	USD
CY2016	us-gaap	Business Combination Acquisition Related Costs BusinessCombinationAcquisitionRelatedCosts	0	USD
CY2017	us-gaap	Business Combination Acquisition Related Costs BusinessCombinationAcquisitionRelatedCosts	14618000	USD
CY2015	us-gaap	Capital Expenditures Incurred But Not Yet Paid CapitalExpendituresIncurredButNotYetPaid	35248000	USD
CY2016	us-gaap	Capital Expenditures Incurred But Not Yet Paid CapitalExpendituresIncurredButNotYetPaid	30252000	USD
CY2017	us-gaap	Capital Expenditures Incurred But Not Yet Paid CapitalExpendituresIncurredButNotYetPaid	31157000	USD
CY2016Q4	us-gaap	Capital Lease Obligations CapitalLeaseObligations	65435000	USD
CY2017Q4	us-gaap	Capital Lease Obligations CapitalLeaseObligations	62148000	USD
CY2014Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	22143000	USD
CY2015Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	10484000	USD
CY2016Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	8507000	USD
CY2017Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	16172000	USD
CY2015	us-gaap	Cash And Cash Equivalents Period Increase Decrease CashAndCashEquivalentsPeriodIncreaseDecrease	-11659000	USD
CY2016	us-gaap	Cash And Cash Equivalents Period Increase Decrease CashAndCashEquivalentsPeriodIncreaseDecrease	-1977000	USD
CY2017	us-gaap	Cash And Cash Equivalents Period Increase Decrease CashAndCashEquivalentsPeriodIncreaseDecrease	7665000	USD
CY2016Q4	us-gaap	Commitments And Contingencies CommitmentsAndContingencies		USD
CY2017Q4	us-gaap	Commitments And Contingencies CommitmentsAndContingencies		USD
CY2015	us-gaap	Common Stock Dividends Per Share Cash Paid CommonStockDividendsPerShareCashPaid	1.32
CY2016	us-gaap	Common Stock Dividends Per Share Cash Paid CommonStockDividendsPerShareCashPaid	1.37
CY2017	us-gaap	Common Stock Dividends Per Share Cash Paid CommonStockDividendsPerShareCashPaid	1.43
CY2016Q4	us-gaap	Common Stock No Par Value CommonStockNoParValue	0
CY2017Q4	us-gaap	Common Stock No Par Value CommonStockNoParValue	0
CY2016Q4	us-gaap	Common Stock Shares Authorized CommonStockSharesAuthorized	200000000	shares
CY2017Q4	us-gaap	Common Stock Shares Authorized CommonStockSharesAuthorized	200000000	shares
CY2016Q4	us-gaap	Common Stock Shares Outstanding CommonStockSharesOutstanding	64187934	shares
CY2017Q4	us-gaap	Common Stock Shares Outstanding CommonStockSharesOutstanding	65494333	shares
CY2016Q4	us-gaap	Common Stock Value CommonStockValue	1075281000	USD
CY2017Q4	us-gaap	Common Stock Value CommonStockValue	1133448000	USD
CY2015	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	124465000	USD
CY2016	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	136310000	USD
CY2017	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	115394000	USD
CY2015	us-gaap	Comprehensive Income Net Of Tax Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest	90000	USD
CY2016Q1	us-gaap	Comprehensive Income Net Of Tax Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest	16000	USD
CY2016Q2	us-gaap	Comprehensive Income Net Of Tax Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest	33000	USD
CY2016Q3	us-gaap	Comprehensive Income Net Of Tax Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest	27000	USD
CY2016Q4	us-gaap	Comprehensive Income Net Of Tax Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest	12000	USD
CY2016	us-gaap	Comprehensive Income Net Of Tax Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest	88000	USD
CY2017Q1	us-gaap	Comprehensive Income Net Of Tax Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest	21000	USD
CY2017Q2	us-gaap	Comprehensive Income Net Of Tax Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest	-49000	USD
CY2017Q3	us-gaap	Comprehensive Income Net Of Tax Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest	7000	USD
CY2017Q4	us-gaap	Comprehensive Income Net Of Tax Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest	37000	USD
CY2017	us-gaap	Comprehensive Income Net Of Tax Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest	16000	USD
CY2015	us-gaap	Comprehensive Income Net Of Tax Including Portion Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest	124555000	USD
CY2016	us-gaap	Comprehensive Income Net Of Tax Including Portion Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest	136398000	USD
CY2017	us-gaap	Comprehensive Income Net Of Tax Including Portion Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest	115410000	USD
CY2015	us-gaap	Costs And Expenses CostsAndExpenses	1231562000	USD
CY2016Q1	us-gaap	Costs And Expenses CostsAndExpenses	312088000	USD
CY2016Q2	us-gaap	Costs And Expenses CostsAndExpenses	257247000	USD
CY2016Q3	us-gaap	Costs And Expenses CostsAndExpenses	263755000	USD
CY2016Q4	us-gaap	Costs And Expenses CostsAndExpenses	319590000	USD
CY2016	us-gaap	Costs And Expenses CostsAndExpenses	1152680000	USD
CY2017Q1	us-gaap	Costs And Expenses CostsAndExpenses	321084000	USD
CY2017Q2	us-gaap	Costs And Expenses CostsAndExpenses	258404000	USD
CY2017Q3	us-gaap	Costs And Expenses CostsAndExpenses	266054000	USD
CY2017Q4	us-gaap	Costs And Expenses CostsAndExpenses	315878000	USD
CY2017	us-gaap	Costs And Expenses CostsAndExpenses	1161420000	USD
CY2015	us-gaap	Current Income Tax Expense Benefit CurrentIncomeTaxExpenseBenefit	12212000	USD
CY2016	us-gaap	Current Income Tax Expense Benefit CurrentIncomeTaxExpenseBenefit	-46457000	USD
CY2017	us-gaap	Current Income Tax Expense Benefit CurrentIncomeTaxExpenseBenefit	13101000	USD
CY2015Q4	us-gaap	Debt Instrument Interest Rate Stated Percentage DebtInstrumentInterestRateStatedPercentage	0.0129
CY2016Q4	us-gaap	Debt Instrument Interest Rate Stated Percentage DebtInstrumentInterestRateStatedPercentage	0.0181
CY2017Q4	us-gaap	Debt Instrument Interest Rate Stated Percentage DebtInstrumentInterestRateStatedPercentage	0.0236
CY2016Q4	us-gaap	Debt Instrument Unamortized Discount DebtInstrumentUnamortizedDiscount	792000	USD
CY2017Q4	us-gaap	Debt Instrument Unamortized Discount DebtInstrumentUnamortizedDiscount	626000	USD
CY2015	us-gaap	Deferred Income Tax Expense Benefit DeferredIncomeTaxExpenseBenefit	55237000	USD
CY2016	us-gaap	Deferred Income Tax Expense Benefit DeferredIncomeTaxExpenseBenefit	124543000	USD
CY2017	us-gaap	Deferred Income Tax Expense Benefit DeferredIncomeTaxExpenseBenefit	69657000	USD
CY2016Q4	us-gaap	Deferred Income Tax Liabilities DeferredIncomeTaxLiabilities	1048275000	USD
CY2017Q4	us-gaap	Deferred Income Tax Liabilities DeferredIncomeTaxLiabilities	693216000	USD
CY2016Q4	us-gaap	Deferred Tax Assets Derivative Instruments DeferredTaxAssetsDerivativeInstruments	31872000	USD
CY2017Q4	us-gaap	Deferred Tax Assets Derivative Instruments DeferredTaxAssetsDerivativeInstruments	23364000	USD
CY2016Q4	us-gaap	Deferred Tax Assets Gross DeferredTaxAssetsGross	215293000	USD
CY2017Q4	us-gaap	Deferred Tax Assets Gross DeferredTaxAssetsGross	237568000	USD
CY2016Q4	us-gaap	Deferred Tax Assets Net DeferredTaxAssetsNet	207347000	USD
CY2017Q4	us-gaap	Deferred Tax Assets Net DeferredTaxAssetsNet	226586000	USD
CY2016Q4	us-gaap	Deferred Tax Assets Other DeferredTaxAssetsOther	22908000	USD
CY2017Q4	us-gaap	Deferred Tax Assets Other DeferredTaxAssetsOther	15892000	USD
CY2016Q4	us-gaap	Deferred Tax Assets Regulatory Assets And Liabilities DeferredTaxAssetsRegulatoryAssetsAndLiabilities	6604000	USD
CY2017Q4	us-gaap	Deferred Tax Assets Regulatory Assets And Liabilities DeferredTaxAssetsRegulatoryAssetsAndLiabilities	105508000	USD
CY2016Q4	us-gaap	Deferred Tax Assets Tax Credit Carryforwards DeferredTaxAssetsTaxCreditCarryforwards	27931000	USD
CY2017Q4	us-gaap	Deferred Tax Assets Tax Credit Carryforwards DeferredTaxAssetsTaxCreditCarryforwards	23042000	USD
CY2016Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Other DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsOther	11141000	USD
CY2017Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Other DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsOther	7080000	USD
CY2016Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Pensions DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsPensions	80230000	USD
CY2017Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Pensions DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsPensions	41944000	USD
CY2016Q4	us-gaap	Deferred Tax Assets Valuation Allowance DeferredTaxAssetsValuationAllowance	7946000	USD
CY2017Q4	us-gaap	Deferred Tax Assets Valuation Allowance DeferredTaxAssetsValuationAllowance	10982000	USD
CY2016Q4	us-gaap	Deferred Tax Liabilities DeferredTaxLiabilities	840928000	USD
CY2017Q4	us-gaap	Deferred Tax Liabilities DeferredTaxLiabilities	466630000	USD
CY2016Q4	us-gaap	Deferred Tax Liabilities Derivatives DeferredTaxLiabilitiesDerivatives	31871000	USD
CY2017Q4	us-gaap	Deferred Tax Liabilities Derivatives DeferredTaxLiabilitiesDerivatives	23364000	USD
CY2016Q4	us-gaap	Deferred Tax Liabilities Noncurrent DeferredTaxLiabilitiesNoncurrent	840928000	USD
CY2017Q4	us-gaap	Deferred Tax Liabilities Noncurrent DeferredTaxLiabilitiesNoncurrent	466630000	USD
CY2016Q4	us-gaap	Deferred Tax Liabilities Other DeferredTaxLiabilitiesOther	8298000	USD
CY2016Q1	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.92
CY2017Q4	us-gaap	Deferred Tax Liabilities Other DeferredTaxLiabilitiesOther	5806000	USD
CY2016Q4	us-gaap	Deferred Tax Liabilities Property Plant And Equipment DeferredTaxLiabilitiesPropertyPlantAndEquipment	812916000	USD
CY2017Q4	us-gaap	Deferred Tax Liabilities Property Plant And Equipment DeferredTaxLiabilitiesPropertyPlantAndEquipment	494783000	USD
CY2016Q4	us-gaap	Deferred Tax Liabilities Regulatory Assets DeferredTaxLiabilitiesRegulatoryAssets	30183000	USD
CY2017Q4	us-gaap	Deferred Tax Liabilities Regulatory Assets DeferredTaxLiabilitiesRegulatoryAssets	16695000	USD
CY2017	us-gaap	Defined Benefit Plan Effect Of One Percentage Point Decrease On Accumulated Postretirement Benefit Obligation1 DefinedBenefitPlanEffectOfOnePercentagePointDecreaseOnAccumulatedPostretirementBenefitObligation1	5200000	USD
CY2017	us-gaap	Defined Benefit Plan Effect Of One Percentage Point Decrease On Service And Interest Cost Components1 DefinedBenefitPlanEffectOfOnePercentagePointDecreaseOnServiceAndInterestCostComponents1	600000	USD
CY2017	us-gaap	Defined Benefit Plan Effect Of One Percentage Point Increase On Accumulated Postretirement Benefit Obligation DefinedBenefitPlanEffectOfOnePercentagePointIncreaseOnAccumulatedPostretirementBenefitObligation	6600000	USD
CY2017	us-gaap	Defined Benefit Plan Effect Of One Percentage Point Increase On Service And Interest Cost Components DefinedBenefitPlanEffectOfOnePercentagePointIncreaseOnServiceAndInterestCostComponents	800000	USD
CY2015	us-gaap	Defined Contribution Plan Cost Recognized DefinedContributionPlanCostRecognized	8011000	USD
CY2016	us-gaap	Defined Contribution Plan Cost Recognized DefinedContributionPlanCostRecognized	8710000	USD
CY2017	us-gaap	Defined Contribution Plan Cost Recognized DefinedContributionPlanCostRecognized	9075000	USD
CY2015	us-gaap	Depreciation And Amortization DepreciationAndAmortization	695000	USD
CY2016	us-gaap	Depreciation And Amortization DepreciationAndAmortization	769000	USD
CY2017	us-gaap	Depreciation And Amortization DepreciationAndAmortization	740000	USD
CY2015	us-gaap	Depreciation Depletion And Amortization DepreciationDepletionAndAmortization	147835000	USD
CY2016	us-gaap	Depreciation Depletion And Amortization DepreciationDepletionAndAmortization	164925000	USD
CY2017	us-gaap	Depreciation Depletion And Amortization DepreciationDepletionAndAmortization	175655000	USD
CY2016Q4	us-gaap	Derivative Assets Liabilities At Fair Value Net DerivativeAssetsLiabilitiesAtFairValueNet	-44432000	USD
CY2017Q4	us-gaap	Derivative Assets Liabilities At Fair Value Net DerivativeAssetsLiabilitiesAtFairValueNet	-47553000	USD
CY2016Q4	us-gaap	Derivative Fair Value Amount Offset Against Collateral Net DerivativeFairValueAmountOffsetAgainstCollateralNet	44758000	USD
CY2017Q4	us-gaap	Derivative Fair Value Amount Offset Against Collateral Net DerivativeFairValueAmountOffsetAgainstCollateralNet	62408000	USD
CY2016Q4	us-gaap	Derivative Fair Value Of Derivative Asset DerivativeFairValueOfDerivativeAsset	61191000	USD
CY2017Q4	us-gaap	Derivative Fair Value Of Derivative Asset DerivativeFairValueOfDerivativeAsset	51506000	USD
CY2016Q4	us-gaap	Derivative Fair Value Of Derivative Liability DerivativeFairValueOfDerivativeLiability	150381000	USD
CY2017Q4	us-gaap	Derivative Fair Value Of Derivative Liability DerivativeFairValueOfDerivativeLiability	161467000	USD
CY2016Q4	us-gaap	Derivative Instruments And Hedges Liabilities DerivativeInstrumentsAndHedgesLiabilities	6025000	USD
CY2017Q4	us-gaap	Derivative Instruments And Hedges Liabilities DerivativeInstrumentsAndHedgesLiabilities	34447000	USD
CY2016Q4	us-gaap	Derivative Instruments And Hedges Liabilities Noncurrent DerivativeInstrumentsAndHedgesLiabilitiesNoncurrent	28705000	USD
CY2017Q4	us-gaap	Derivative Instruments And Hedges Liabilities Noncurrent DerivativeInstrumentsAndHedgesLiabilitiesNoncurrent	1522000	USD
CY2016Q4	us-gaap	Derivative Liabilities Current DerivativeLiabilitiesCurrent	7035000	USD
CY2017Q4	us-gaap	Derivative Liabilities Current DerivativeLiabilitiesCurrent	8848000	USD
CY2015	us-gaap	Discontinued Operation Gain Loss From Disposal Of Discontinued Operation Before Income Tax DiscontinuedOperationGainLossFromDisposalOfDiscontinuedOperationBeforeIncomeTax	777000	USD
CY2016	us-gaap	Discontinued Operation Gain Loss From Disposal Of Discontinued Operation Before Income Tax DiscontinuedOperationGainLossFromDisposalOfDiscontinuedOperationBeforeIncomeTax	0	USD
CY2017	us-gaap	Discontinued Operation Gain Loss From Disposal Of Discontinued Operation Before Income Tax DiscontinuedOperationGainLossFromDisposalOfDiscontinuedOperationBeforeIncomeTax	0	USD
	us-gaap	Discontinued Operation Gain Loss On Disposal Of Discontinued Operation Net Of Tax DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax	74800000	USD
CY2014	us-gaap	Discontinued Operation Gain Loss On Disposal Of Discontinued Operation Net Of Tax DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax	69700000	USD
CY2015	us-gaap	Discontinued Operation Income Loss From Discontinued Operation Before Income Tax DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax	706000	USD
CY2015	us-gaap	Discontinued Operation Tax Effect Of Discontinued Operation DiscontinuedOperationTaxEffectOfDiscontinuedOperation	-4441000	USD
CY2015Q2	us-gaap	Disposal Group Including Discontinued Operation Consideration DisposalGroupIncludingDiscontinuedOperationConsideration	335000000	USD
CY2015	us-gaap	Disposal Group Including Discontinued Operation Revenue DisposalGroupIncludingDiscontinuedOperationRevenue	0	USD
CY2015	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	1.98
CY2016	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	2.16
CY2017	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	1.80
CY2015	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	1.97
CY2015	us-gaap	Employee Service Share Based Compensation Tax Benefit From Exercise Of Stock Options EmployeeServiceShareBasedCompensationTaxBenefitFromExerciseOfStockOptions	0	USD
CY2016	us-gaap	Employee Service Share Based Compensation Tax Benefit From Exercise Of Stock Options EmployeeServiceShareBasedCompensationTaxBenefitFromExerciseOfStockOptions	1597000	USD
CY2017	us-gaap	Employee Service Share Based Compensation Tax Benefit From Exercise Of Stock Options EmployeeServiceShareBasedCompensationTaxBenefitFromExerciseOfStockOptions	2348000	USD
CY2016Q4	us-gaap	Energy Related Inventory Natural Gas In Storage EnergyRelatedInventoryNaturalGasInStorage	8029000	USD
CY2017Q4	us-gaap	Energy Related Inventory Natural Gas In Storage EnergyRelatedInventoryNaturalGasInStorage	11739000	USD
CY2017Q4	us-gaap	Equity Method Investment Ownership Percentage EquityMethodInvestmentOwnershipPercentage	1
CY2015	us-gaap	Gain Loss On Investments GainLossOnInvestments	-637000	USD
CY2016	us-gaap	Gain Loss On Investments GainLossOnInvestments	-2152000	USD
CY2017	us-gaap	Gain Loss On Investments GainLossOnInvestments	-4160000	USD
CY2016Q2	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.43
CY2016Q3	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.19
CY2016Q4	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.62
CY2016	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	2.15
CY2017Q1	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.96
CY2017Q2	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.34
CY2017Q3	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.07
CY2017Q4	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.42
CY2017	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	1.79
CY2015	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	0.363
CY2016	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	0.363
CY2017	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	0.417
CY2018Q1	us-gaap	Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	0.21
CY2015	us-gaap	Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	0.350
CY2016	us-gaap	Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	0.350
CY2017	us-gaap	Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	0.350
CY2016	us-gaap	Effective Income Tax Rate Reconciliation Change In Enacted Tax Rate EffectiveIncomeTaxRateReconciliationChangeInEnactedTaxRate	0.000
CY2017	us-gaap	Effective Income Tax Rate Reconciliation Change In Enacted Tax Rate EffectiveIncomeTaxRateReconciliationChangeInEnactedTaxRate	0.051
CY2015	us-gaap	Effective Income Tax Rate Reconciliation Deductions Qualified Production Activities EffectiveIncomeTaxRateReconciliationDeductionsQualifiedProductionActivities	0.006
CY2016	us-gaap	Effective Income Tax Rate Reconciliation Deductions Qualified Production Activities EffectiveIncomeTaxRateReconciliationDeductionsQualifiedProductionActivities	0.000
CY2017	us-gaap	Effective Income Tax Rate Reconciliation Deductions Qualified Production Activities EffectiveIncomeTaxRateReconciliationDeductionsQualifiedProductionActivities	0.006
CY2015	us-gaap	Effective Income Tax Rate Reconciliation Other Adjustments EffectiveIncomeTaxRateReconciliationOtherAdjustments	-0.004
CY2016	us-gaap	Effective Income Tax Rate Reconciliation Other Adjustments EffectiveIncomeTaxRateReconciliationOtherAdjustments	-0.001
CY2017	us-gaap	Effective Income Tax Rate Reconciliation Other Adjustments EffectiveIncomeTaxRateReconciliationOtherAdjustments	-0.005
CY2015	us-gaap	Effective Income Tax Rate Reconciliation Prior Year Income Taxes EffectiveIncomeTaxRateReconciliationPriorYearIncomeTaxes	-0.005
CY2016	us-gaap	Effective Income Tax Rate Reconciliation Prior Year Income Taxes EffectiveIncomeTaxRateReconciliationPriorYearIncomeTaxes	0.000
CY2017	us-gaap	Effective Income Tax Rate Reconciliation Prior Year Income Taxes EffectiveIncomeTaxRateReconciliationPriorYearIncomeTaxes	-0.002
CY2015	us-gaap	Effective Income Tax Rate Reconciliation State And Local Income Taxes EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes	0.005
CY2016	us-gaap	Effective Income Tax Rate Reconciliation State And Local Income Taxes EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes	0.006
CY2017	us-gaap	Effective Income Tax Rate Reconciliation State And Local Income Taxes EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes	0.006
CY2015	us-gaap	Employee Service Share Based Compensation Tax Benefit From Compensation Expense EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense	2420000	USD
CY2016	us-gaap	Employee Service Share Based Compensation Tax Benefit From Compensation Expense EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense	2762000	USD
CY2017	us-gaap	Employee Service Share Based Compensation Tax Benefit From Compensation Expense EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense	2576000	USD
CY2016Q4	us-gaap	Goodwill Goodwill	57672000	USD
CY2017Q4	us-gaap	Goodwill Goodwill	57672000	USD
CY2015	us-gaap	Income Loss From Continuing Operations IncomeLossFromContinuingOperations	118080000	USD
CY2016	us-gaap	Income Loss From Continuing Operations IncomeLossFromContinuingOperations	137228000	USD
CY2015	us-gaap	Income Loss From Continuing Operations Including Portion Attributable To Noncontrolling Interest IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest	118170000	USD
CY2016	us-gaap	Income Loss From Continuing Operations Including Portion Attributable To Noncontrolling Interest IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest	137316000	USD
CY2017	us-gaap	Income Loss From Continuing Operations IncomeLossFromContinuingOperations	115916000	USD
CY2015	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	185619000	USD
CY2016	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	215402000	USD
CY2017	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	198690000	USD
CY2015	us-gaap	Increase Decrease In Accounts Payable IncreaseDecreaseInAccountsPayable	-8138000	USD
CY2016	us-gaap	Increase Decrease In Accounts Payable IncreaseDecreaseInAccountsPayable	5176000	USD
CY2017	us-gaap	Increase Decrease In Accounts Payable IncreaseDecreaseInAccountsPayable	-8162000	USD
CY2015	us-gaap	Increase Decrease In Deposit Other Assets IncreaseDecreaseInDepositOtherAssets	13301000	USD
CY2016	us-gaap	Increase Decrease In Deposit Other Assets IncreaseDecreaseInDepositOtherAssets	-10712000	USD
CY2015	us-gaap	Income Tax Reconciliation Prior Year Income Taxes IncomeTaxReconciliationPriorYearIncomeTaxes	-992000	USD
CY2016	us-gaap	Income Tax Reconciliation Prior Year Income Taxes IncomeTaxReconciliationPriorYearIncomeTaxes	13000	USD
CY2017	us-gaap	Income Tax Reconciliation Prior Year Income Taxes IncomeTaxReconciliationPriorYearIncomeTaxes	-384000	USD
CY2015	us-gaap	Income Tax Reconciliation State And Local Income Taxes IncomeTaxReconciliationStateAndLocalIncomeTaxes	1012000	USD
CY2016	us-gaap	Income Tax Reconciliation State And Local Income Taxes IncomeTaxReconciliationStateAndLocalIncomeTaxes	1316000	USD
CY2017	us-gaap	Income Tax Reconciliation State And Local Income Taxes IncomeTaxReconciliationStateAndLocalIncomeTaxes	1110000	USD
CY2017	us-gaap	Income Loss From Continuing Operations Including Portion Attributable To Noncontrolling Interest IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest	115932000	USD
CY2015	us-gaap	Income Loss From Continuing Operations Per Basic Share IncomeLossFromContinuingOperationsPerBasicShare	1.90
CY2016	us-gaap	Income Loss From Continuing Operations Per Basic Share IncomeLossFromContinuingOperationsPerBasicShare	2.16
CY2017	us-gaap	Income Loss From Continuing Operations Per Basic Share IncomeLossFromContinuingOperationsPerBasicShare	1.80
CY2015	us-gaap	Income Loss From Continuing Operations Per Diluted Share IncomeLossFromContinuingOperationsPerDilutedShare	1.89
CY2016	us-gaap	Income Loss From Continuing Operations Per Diluted Share IncomeLossFromContinuingOperationsPerDilutedShare	2.15
CY2017	us-gaap	Income Loss From Continuing Operations Per Diluted Share IncomeLossFromContinuingOperationsPerDilutedShare	1.79
CY2015	us-gaap	Income Loss From Discontinued Operations Net Of Tax IncomeLossFromDiscontinuedOperationsNetOfTax	5147000	USD
CY2016	us-gaap	Income Loss From Discontinued Operations Net Of Tax IncomeLossFromDiscontinuedOperationsNetOfTax	0	USD
CY2017	us-gaap	Income Loss From Discontinued Operations Net Of Tax IncomeLossFromDiscontinuedOperationsNetOfTax	0	USD
CY2015	us-gaap	Income Loss From Discontinued Operations Net Of Tax Attributable To Reporting Entity IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity	5147000	USD
CY2016	us-gaap	Income Loss From Discontinued Operations Net Of Tax Attributable To Reporting Entity IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity	0	USD
CY2017	us-gaap	Income Loss From Discontinued Operations Net Of Tax Attributable To Reporting Entity IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity	0	USD
CY2015	us-gaap	Income Loss From Discontinued Operations Net Of Tax Per Basic Share IncomeLossFromDiscontinuedOperationsNetOfTaxPerBasicShare	0.08
CY2016	us-gaap	Income Loss From Discontinued Operations Net Of Tax Per Basic Share IncomeLossFromDiscontinuedOperationsNetOfTaxPerBasicShare	0.00
CY2017	us-gaap	Income Loss From Discontinued Operations Net Of Tax Per Basic Share IncomeLossFromDiscontinuedOperationsNetOfTaxPerBasicShare	0.00
CY2015	us-gaap	Income Loss From Discontinued Operations Net Of Tax Per Diluted Share IncomeLossFromDiscontinuedOperationsNetOfTaxPerDilutedShare	0.08
CY2016	us-gaap	Income Loss From Discontinued Operations Net Of Tax Per Diluted Share IncomeLossFromDiscontinuedOperationsNetOfTaxPerDilutedShare	0.00
CY2017	us-gaap	Income Loss From Discontinued Operations Net Of Tax Per Diluted Share IncomeLossFromDiscontinuedOperationsNetOfTaxPerDilutedShare	0.00
CY2015	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	67449000	USD
CY2016	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	78086000	USD
CY2017	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	82758000	USD
CY2016	us-gaap	Income Tax Reconciliation Change In Enacted Tax Rate IncomeTaxReconciliationChangeInEnactedTaxRate	0	USD
CY2017	us-gaap	Income Tax Reconciliation Change In Enacted Tax Rate IncomeTaxReconciliationChangeInEnactedTaxRate	10169000	USD
CY2015	us-gaap	Income Tax Reconciliation Deductions Qualified Production Activities IncomeTaxReconciliationDeductionsQualifiedProductionActivities	1198000	USD
CY2016	us-gaap	Income Tax Reconciliation Deductions Qualified Production Activities IncomeTaxReconciliationDeductionsQualifiedProductionActivities	0	USD
CY2017	us-gaap	Income Tax Reconciliation Deductions Qualified Production Activities IncomeTaxReconciliationDeductionsQualifiedProductionActivities	1119000	USD
CY2015	us-gaap	Income Tax Reconciliation Income Tax Expense Benefit At Federal Statutory Income Tax Rate IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate	64967000	USD
CY2016	us-gaap	Income Tax Reconciliation Income Tax Expense Benefit At Federal Statutory Income Tax Rate IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate	75391000	USD
CY2017	us-gaap	Income Tax Reconciliation Income Tax Expense Benefit At Federal Statutory Income Tax Rate IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate	69542000	USD
CY2015	us-gaap	Income Tax Reconciliation Other Adjustments IncomeTaxReconciliationOtherAdjustments	-698000	USD
CY2016	us-gaap	Income Tax Reconciliation Other Adjustments IncomeTaxReconciliationOtherAdjustments	-334000	USD
CY2017	us-gaap	Income Tax Reconciliation Other Adjustments IncomeTaxReconciliationOtherAdjustments	-1094000	USD
CY2015	us-gaap	Income Taxes Paid IncomeTaxesPaid	27239000	USD
CY2016	us-gaap	Income Taxes Paid IncomeTaxesPaid	5403000	USD
CY2017	us-gaap	Income Taxes Paid IncomeTaxesPaid	5579000	USD
CY2016Q4	us-gaap	Income Taxes Receivable IncomeTaxesReceivable	48265000	USD
CY2017Q4	us-gaap	Income Taxes Receivable IncomeTaxesReceivable	314000	USD
CY2015	us-gaap	Increase Decrease In Accounts And Notes Receivable IncreaseDecreaseInAccountsAndNotesReceivable	10538000	USD
CY2016	us-gaap	Increase Decrease In Accounts And Notes Receivable IncreaseDecreaseInAccountsAndNotesReceivable	17170000	USD
CY2017	us-gaap	Increase Decrease In Accounts And Notes Receivable IncreaseDecreaseInAccountsAndNotesReceivable	9270000	USD
CY2017	us-gaap	Increase Decrease In Deposit Other Assets IncreaseDecreaseInDepositOtherAssets	22394000	USD
CY2016Q4	us-gaap	Liabilities Liabilities	3661279000	USD
CY2015	us-gaap	Increase Decrease In Income Taxes Receivable IncreaseDecreaseInIncomeTaxesReceivable	-19772000	USD
CY2016	us-gaap	Increase Decrease In Income Taxes Receivable IncreaseDecreaseInIncomeTaxesReceivable	33923000	USD
CY2017	us-gaap	Increase Decrease In Income Taxes Receivable IncreaseDecreaseInIncomeTaxesReceivable	-53414000	USD
CY2015	us-gaap	Increase Decrease In Inventories IncreaseDecreaseInInventories	-12208000	USD
CY2016	us-gaap	Increase Decrease In Inventories IncreaseDecreaseInInventories	-834000	USD
CY2017	us-gaap	Increase Decrease In Inventories IncreaseDecreaseInInventories	4767000	USD
CY2015	us-gaap	Increase Decrease In Other Operating Assets IncreaseDecreaseInOtherOperatingAssets	-2338000	USD
CY2016	us-gaap	Increase Decrease In Other Operating Assets IncreaseDecreaseInOtherOperatingAssets	3907000	USD
CY2017	us-gaap	Increase Decrease In Other Operating Assets IncreaseDecreaseInOtherOperatingAssets	2106000	USD
CY2015	us-gaap	Increase Decrease In Other Operating Liabilities IncreaseDecreaseInOtherOperatingLiabilities	-6471000	USD
CY2016	us-gaap	Increase Decrease In Other Operating Liabilities IncreaseDecreaseInOtherOperatingLiabilities	10546000	USD
CY2017	us-gaap	Increase Decrease In Other Operating Liabilities IncreaseDecreaseInOtherOperatingLiabilities	1058000	USD
CY2015	us-gaap	Increase Decrease In Regulatory Assets And Liabilities IncreaseDecreaseInRegulatoryAssetsAndLiabilities	-4569000	USD
CY2016	us-gaap	Increase Decrease In Regulatory Assets And Liabilities IncreaseDecreaseInRegulatoryAssetsAndLiabilities	26245000	USD
CY2017	us-gaap	Increase Decrease In Regulatory Assets And Liabilities IncreaseDecreaseInRegulatoryAssetsAndLiabilities	9144000	USD
CY2015	us-gaap	Incremental Common Shares Attributable To Share Based Payment Arrangements IncrementalCommonSharesAttributableToShareBasedPaymentArrangements	407000	shares
CY2016	us-gaap	Incremental Common Shares Attributable To Share Based Payment Arrangements IncrementalCommonSharesAttributableToShareBasedPaymentArrangements	412000	shares
CY2017	us-gaap	Incremental Common Shares Attributable To Share Based Payment Arrangements IncrementalCommonSharesAttributableToShareBasedPaymentArrangements	310000	shares
CY2015	us-gaap	Interest Expense InterestExpense	79968000	USD
CY2016	us-gaap	Interest Expense InterestExpense	86496000	USD
CY2017	us-gaap	Interest Expense InterestExpense	95361000	USD
CY2015	us-gaap	Interest Expense Other InterestExpenseOther	473000	USD
CY2016	us-gaap	Interest Expense Other InterestExpenseOther	634000	USD
CY2017	us-gaap	Interest Expense Other InterestExpenseOther	831000	USD
CY2015	us-gaap	Interest Paid InterestPaid	79673000	USD
CY2016	us-gaap	Interest Paid InterestPaid	86319000	USD
CY2017	us-gaap	Interest Paid InterestPaid	95499000	USD
CY2016Q4	us-gaap	Interest Payable Current InterestPayableCurrent	15869000	USD
CY2017Q4	us-gaap	Interest Payable Current InterestPayableCurrent	16351000	USD
CY2016Q4	us-gaap	Inventory Net InventoryNet	53314000	USD
CY2017Q4	us-gaap	Inventory Net InventoryNet	58075000	USD
CY2016Q4	us-gaap	Inventory Raw Materials And Supplies InventoryRawMaterialsAndSupplies	40700000	USD
CY2017Q4	us-gaap	Inventory Raw Materials And Supplies InventoryRawMaterialsAndSupplies	41493000	USD
CY2015	us-gaap	Investment Income Interest InvestmentIncomeInterest	653000	USD
CY2016	us-gaap	Investment Income Interest InvestmentIncomeInterest	1823000	USD
CY2017	us-gaap	Investment Income Interest InvestmentIncomeInterest	2162000	USD
CY2016Q4	us-gaap	Investments And Other Noncurrent Assets InvestmentsAndOtherNoncurrentAssets	72224000	USD
CY2017Q4	us-gaap	Investments And Other Noncurrent Assets InvestmentsAndOtherNoncurrentAssets	83912000	USD
CY2016Q4	us-gaap	Investments In Affiliates Subsidiaries Associates And Joint Ventures InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures	11547000	USD
CY2017Q4	us-gaap	Investments In Affiliates Subsidiaries Associates And Joint Ventures InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures	11547000	USD
CY2017Q4	us-gaap	Jointly Owned Utility Plant Proportionate Ownership Share JointlyOwnedUtilityPlantProportionateOwnershipShare	0.15
CY2017Q4	us-gaap	Junior Subordinated Debenture Owed To Unconsolidated Subsidiary Trust JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust	51500000	USD
CY1997Q4	us-gaap	Junior Subordinated Debenture Owed To Unconsolidated Subsidiary Trust JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust	51500000	USD
CY2016Q4	us-gaap	Junior Subordinated Debenture Owed To Unconsolidated Subsidiary Trust Noncurrent JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrustNoncurrent	51547000	USD
CY2017Q4	us-gaap	Junior Subordinated Debenture Owed To Unconsolidated Subsidiary Trust Noncurrent JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrustNoncurrent	51547000	USD
CY2017Q3	us-gaap	Net Income Loss NetIncomeLoss	4451000	USD
CY2017Q4	us-gaap	Net Income Loss NetIncomeLoss	27578000	USD
CY2017Q4	us-gaap	Liabilities Liabilities	3784248000	USD
CY2016Q4	us-gaap	Liabilities And Stockholders Equity LiabilitiesAndStockholdersEquity	5309755000	USD
CY2017Q4	us-gaap	Liabilities And Stockholders Equity LiabilitiesAndStockholdersEquity	5514732000	USD
CY2016Q4	us-gaap	Liabilities Current LiabilitiesCurrent	407528000	USD
CY2017Q4	us-gaap	Liabilities Current LiabilitiesCurrent	697502000	USD
CY2017	us-gaap	Long Term Contract For Purchase Of Electric Power Amount Of Long Term Debt Or Lease Obligation Outstanding LongTermContractForPurchaseOfElectricPowerAmountOfLongTermDebtOrLeaseObligationOutstanding	63500000	USD
CY2016Q4	us-gaap	Long Term Debt And Capital Lease Obligations LongTermDebtAndCapitalLeaseObligations	1678717000	USD
CY2017Q4	us-gaap	Long Term Debt And Capital Lease Obligations LongTermDebtAndCapitalLeaseObligations	1491799000	USD
CY2016Q4	us-gaap	Long Term Debt And Capital Lease Obligations Current LongTermDebtAndCapitalLeaseObligationsCurrent	3287000	USD
CY2017Q4	us-gaap	Long Term Debt And Capital Lease Obligations Current LongTermDebtAndCapitalLeaseObligationsCurrent	277438000	USD
CY2016Q4	us-gaap	Long Term Pollution Control Bond LongTermPollutionControlBond	-83700000	USD
CY2017Q4	us-gaap	Long Term Pollution Control Bond LongTermPollutionControlBond	-83700000	USD
CY2016Q4	us-gaap	Minority Interest MinorityInterest	-251000	USD
CY2017Q4	us-gaap	Minority Interest MinorityInterest	656000	USD
CY2015	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	528000	USD
CY2016	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	72222000	USD
CY2017	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	31470000	USD
CY2015	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-387827000	USD
CY2016	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-432466000	USD
CY2017	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-434103000	USD
CY2015	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	375640000	USD
CY2016	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	358267000	USD
CY2017	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	410298000	USD
CY2015	us-gaap	Net Income Loss NetIncomeLoss	123227000	USD
CY2016Q1	us-gaap	Net Income Loss NetIncomeLoss	57649000	USD
CY2016Q2	us-gaap	Net Income Loss NetIncomeLoss	27254000	USD
CY2016Q3	us-gaap	Net Income Loss NetIncomeLoss	12234000	USD
CY2016Q4	us-gaap	Net Income Loss NetIncomeLoss	40091000	USD
CY2016	us-gaap	Net Income Loss NetIncomeLoss	137228000	USD
CY2017Q1	us-gaap	Net Income Loss NetIncomeLoss	62116000	USD
CY2017Q2	us-gaap	Net Income Loss NetIncomeLoss	21771000	USD
CY2017	us-gaap	Net Income Loss NetIncomeLoss	115916000	USD
CY2016Q4	us-gaap	Number Of Foreign Currency Derivatives Held NumberOfForeignCurrencyDerivativesHeld	21
CY2017Q4	us-gaap	Number Of Foreign Currency Derivatives Held NumberOfForeignCurrencyDerivativesHeld	18
CY2017	us-gaap	Number Of Reportable Segments NumberOfReportableSegments	2	Reportable_Segments
CY2015	us-gaap	Operating Income Loss OperatingIncomeLoss	253214000	USD
CY2016Q1	us-gaap	Operating Income Loss OperatingIncomeLoss	106085000	USD
CY2016Q2	us-gaap	Operating Income Loss OperatingIncomeLoss	61591000	USD
CY2016Q3	us-gaap	Operating Income Loss OperatingIncomeLoss	39594000	USD
CY2016Q4	us-gaap	Operating Income Loss OperatingIncomeLoss	82533000	USD
CY2016	us-gaap	Operating Income Loss OperatingIncomeLoss	289803000	USD
CY2017Q1	us-gaap	Operating Income Loss OperatingIncomeLoss	115386000	USD
CY2017Q2	us-gaap	Operating Income Loss OperatingIncomeLoss	56097000	USD
CY2017Q3	us-gaap	Operating Income Loss OperatingIncomeLoss	31042000	USD
CY2017Q4	us-gaap	Operating Income Loss OperatingIncomeLoss	81984000	USD
CY2017	us-gaap	Operating Income Loss OperatingIncomeLoss	284509000	USD
CY2015	us-gaap	Other Amortization Of Deferred Charges OtherAmortizationOfDeferredCharges	21358000	USD
CY2016	us-gaap	Other Amortization Of Deferred Charges OtherAmortizationOfDeferredCharges	16835000	USD
CY2017	us-gaap	Other Amortization Of Deferred Charges OtherAmortizationOfDeferredCharges	11741000	USD
CY2016Q4	us-gaap	Other Assets Current OtherAssetsCurrent	49625000	USD
CY2017Q4	us-gaap	Other Assets Current OtherAssetsCurrent	52318000	USD
CY2016Q4	us-gaap	Other Assets Miscellaneous Noncurrent OtherAssetsMiscellaneousNoncurrent	5326000	USD
CY2017Q4	us-gaap	Other Assets Miscellaneous Noncurrent OtherAssetsMiscellaneousNoncurrent	9828000	USD
CY2016Q4	us-gaap	Other Assets Noncurrent OtherAssetsNoncurrent	141443000	USD
CY2017Q4	us-gaap	Other Assets Noncurrent OtherAssetsNoncurrent	153131000	USD
CY2015	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	1238000	USD
CY2016	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	-918000	USD
CY2017	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	-522000	USD
CY2015	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	-1238000	USD
CY2016	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	918000	USD
CY2017	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	522000	USD
CY2015	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax	667000	USD
CY2016	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax	-495000	USD
CY2017	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax	-281000	USD
CY2015	us-gaap	Other Cost And Expense Operating OtherCostAndExpenseOperating	29526000	USD
CY2016	us-gaap	Other Cost And Expense Operating OtherCostAndExpenseOperating	25501000	USD
CY2017	us-gaap	Other Cost And Expense Operating OtherCostAndExpenseOperating	25650000	USD
CY2015	us-gaap	Other Income OtherIncome	905000	USD
CY2016	us-gaap	Other Income OtherIncome	624000	USD
CY2017	us-gaap	Other Income OtherIncome	1104000	USD
CY2016Q4	us-gaap	Other Inventory OtherInventory	4585000	USD
CY2017Q4	us-gaap	Other Inventory OtherInventory	4843000	USD
CY2016Q4	us-gaap	Other Liabilities Current OtherLiabilitiesCurrent	64579000	USD
CY2017Q4	us-gaap	Other Liabilities Current OtherLiabilitiesCurrent	64911000	USD
CY2016Q4	us-gaap	Other Liabilities Noncurrent OtherLiabilitiesNoncurrent	153319000	USD
CY2017Q4	us-gaap	Other Liabilities Noncurrent OtherLiabilitiesNoncurrent	143577000	USD
CY2015	us-gaap	Other Nonoperating Income Expense OtherNonoperatingIncomeExpense	9300000	USD
CY2016	us-gaap	Other Nonoperating Income Expense OtherNonoperatingIncomeExpense	10078000	USD
CY2017	us-gaap	Other Nonoperating Income Expense OtherNonoperatingIncomeExpense	7063000	USD
CY2015	us-gaap	Other Operating Activities Cash Flow Statement OtherOperatingActivitiesCashFlowStatement	-517000	USD
CY2016	us-gaap	Other Operating Activities Cash Flow Statement OtherOperatingActivitiesCashFlowStatement	5557000	USD
CY2017	us-gaap	Other Operating Activities Cash Flow Statement OtherOperatingActivitiesCashFlowStatement	1860000	USD
CY2015	us-gaap	Other Sales Revenue Net OtherSalesRevenueNet	28685000	USD
CY2016	us-gaap	Other Sales Revenue Net OtherSalesRevenueNet	23569000	USD
CY2017	us-gaap	Other Sales Revenue Net OtherSalesRevenueNet	22543000	USD
CY2015	us-gaap	Payments For Proceeds From Investments PaymentsForProceedsFromInvestments	0	USD
CY2016	us-gaap	Payments For Proceeds From Investments PaymentsForProceedsFromInvestments	0	USD
CY2017	us-gaap	Payments For Proceeds From Investments PaymentsForProceedsFromInvestments	-1915000	USD
CY2015	us-gaap	Payments For Proceeds From Other Investing Activities PaymentsForProceedsFromOtherInvestingActivities	4007000	USD
CY2016	us-gaap	Payments For Proceeds From Other Investing Activities PaymentsForProceedsFromOtherInvestingActivities	7631000	USD
CY2017	us-gaap	Payments For Proceeds From Other Investing Activities PaymentsForProceedsFromOtherInvestingActivities	6299000	USD
CY2015	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	2920000	USD
CY2016	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	0	USD
CY2017	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	0	USD
CY2000	us-gaap	Payments For Repurchase Of Trust Preferred Securities PaymentsForRepurchaseOfTrustPreferredSecurities	10000000	USD
CY2015	us-gaap	Payments Of Dividends PaymentsOfDividends	82397000	USD
CY2016	us-gaap	Payments Of Dividends PaymentsOfDividends	87154000	USD
CY2017	us-gaap	Payments Of Dividends PaymentsOfDividends	92460000	USD
CY2015	us-gaap	Payments To Acquire Investments PaymentsToAcquireInvestments	1944000	USD
CY2016	us-gaap	Payments To Acquire Investments PaymentsToAcquireInvestments	13097000	USD
CY2017	us-gaap	Payments To Acquire Investments PaymentsToAcquireInvestments	13680000	USD
CY2015	us-gaap	Payments To Acquire Notes Receivable PaymentsToAcquireNotesReceivable	2307000	USD
CY2016	us-gaap	Payments To Acquire Notes Receivable PaymentsToAcquireNotesReceivable	10094000	USD
CY2017	us-gaap	Payments To Acquire Notes Receivable PaymentsToAcquireNotesReceivable	3700000	USD
CY2015	us-gaap	Payments To Acquire Other Property Plant And Equipment PaymentsToAcquireOtherPropertyPlantAndEquipment	394310000	USD
CY2016	us-gaap	Payments To Acquire Other Property Plant And Equipment PaymentsToAcquireOtherPropertyPlantAndEquipment	406997000	USD
CY2017	us-gaap	Payments To Acquire Other Property Plant And Equipment PaymentsToAcquireOtherPropertyPlantAndEquipment	416619000	USD
CY2015	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	393425000	USD
CY2016	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	406644000	USD
CY2017	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	412339000	USD
CY2015	us-gaap	Pension And Other Postretirement Benefit Expense PensionAndOtherPostretirementBenefitExpense	37050000	USD
CY2016	us-gaap	Pension And Other Postretirement Benefit Expense PensionAndOtherPostretirementBenefitExpense	38786000	USD
CY2017	us-gaap	Pension And Other Postretirement Benefit Expense PensionAndOtherPostretirementBenefitExpense	37074000	USD
CY2016Q4	us-gaap	Pension And Other Postretirement Defined Benefit Plans Current Liabilities PensionAndOtherPostretirementDefinedBenefitPlansCurrentLiabilities	10994000	USD
CY2017Q4	us-gaap	Pension And Other Postretirement Defined Benefit Plans Current Liabilities PensionAndOtherPostretirementDefinedBenefitPlansCurrentLiabilities	11544000	USD
CY2016Q4	us-gaap	Pension And Other Postretirement Defined Benefit Plans Liabilities Noncurrent PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent	226552000	USD
CY2017Q4	us-gaap	Pension And Other Postretirement Defined Benefit Plans Liabilities Noncurrent PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent	203566000	USD
CY2015	us-gaap	Pension Contributions PensionContributions	12000000	USD
CY2016	us-gaap	Pension Contributions PensionContributions	12000000	USD
CY2017	us-gaap	Pension Contributions PensionContributions	22000000	USD
CY2017Q4	us-gaap	Preferred Stock Shares Authorized PreferredStockSharesAuthorized	10000000	shares
CY2016Q4	us-gaap	Preferred Stock Shares Outstanding PreferredStockSharesOutstanding	0	shares
CY2017Q4	us-gaap	Preferred Stock Shares Outstanding PreferredStockSharesOutstanding	0	shares
	us-gaap	Proceeds From Divestiture Of Businesses ProceedsFromDivestitureOfBusinesses	143700000	USD
CY2015	us-gaap	Proceeds From Divestiture Of Businesses Net Of Cash Divested ProceedsFromDivestitureOfBusinessesNetOfCashDivested	13856000	USD
CY2016	us-gaap	Proceeds From Divestiture Of Businesses Net Of Cash Divested ProceedsFromDivestitureOfBusinessesNetOfCashDivested	0	USD
CY2017	us-gaap	Proceeds From Divestiture Of Businesses Net Of Cash Divested ProceedsFromDivestitureOfBusinessesNetOfCashDivested	0	USD
CY2015	us-gaap	Proceeds From Income Tax Refunds ProceedsFromIncomeTaxRefunds	37200000	USD
CY2016	us-gaap	Proceeds From Issuance Of Common Stock ProceedsFromIssuanceOfCommonStock	66953000	USD
CY2016	us-gaap	Proceeds From Income Tax Refunds ProceedsFromIncomeTaxRefunds	18861000	USD
CY2017	us-gaap	Proceeds From Income Tax Refunds ProceedsFromIncomeTaxRefunds	47086000	USD
CY2015	us-gaap	Proceeds From Issuance Of Common Stock ProceedsFromIssuanceOfCommonStock	1560000	USD
CY2015	us-gaap	Proceeds From Payments For Other Financing Activities ProceedsFromPaymentsForOtherFinancingActivities	-11379000	USD
CY2017	us-gaap	Proceeds From Issuance Of Common Stock ProceedsFromIssuanceOfCommonStock	56380000	USD
CY2015	us-gaap	Proceeds From Issuance Of Long Term Debt ProceedsFromIssuanceOfLongTermDebt	100000000	USD
CY2016	us-gaap	Proceeds From Issuance Of Long Term Debt ProceedsFromIssuanceOfLongTermDebt	245000000	USD
CY2017	us-gaap	Proceeds From Issuance Of Long Term Debt ProceedsFromIssuanceOfLongTermDebt	90000000	USD
CY2017Q4	us-gaap	Public Utilities Property Plant And Equipment Construction Work In Progress PublicUtilitiesPropertyPlantAndEquipmentConstructionWorkInProgress	157839000	USD
CY2016Q4	us-gaap	Public Utilities Property Plant And Equipment Net PublicUtilitiesPropertyPlantAndEquipmentNet	4147500000	USD
CY2017Q4	us-gaap	Public Utilities Property Plant And Equipment Net PublicUtilitiesPropertyPlantAndEquipmentNet	4398810000	USD
CY2016Q4	us-gaap	Public Utilities Property Plant And Equipment Plant In Service PublicUtilitiesPropertyPlantAndEquipmentPlantInService	5506499000	USD
CY2017Q4	us-gaap	Public Utilities Property Plant And Equipment Plant In Service PublicUtilitiesPropertyPlantAndEquipmentPlantInService	5853308000	USD
CY2015	us-gaap	Real Estate Tax Expense RealEstateTaxExpense	35948000	USD
CY2017	us-gaap	Unrecognized Tax Benefits Income Tax Penalties And Interest Expense UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense	0	USD
CY2016	us-gaap	Proceeds From Payments For Other Financing Activities ProceedsFromPaymentsForOtherFinancingActivities	-4410000	USD
CY2017	us-gaap	Proceeds From Payments For Other Financing Activities ProceedsFromPaymentsForOtherFinancingActivities	-4163000	USD
CY2015	us-gaap	Proceeds From Repayments Of Short Term Debt ProceedsFromRepaymentsOfShortTermDebt	0	USD
CY2016	us-gaap	Proceeds From Repayments Of Short Term Debt ProceedsFromRepaymentsOfShortTermDebt	15000000	USD
CY2017	us-gaap	Proceeds From Repayments Of Short Term Debt ProceedsFromRepaymentsOfShortTermDebt	-15000000	USD
CY2015	us-gaap	Proceeds From Sale And Collection Of Notes Receivable ProceedsFromSaleAndCollectionOfNotesReceivable	0	USD
CY2016	us-gaap	Proceeds From Sale And Collection Of Notes Receivable ProceedsFromSaleAndCollectionOfNotesReceivable	5000000	USD
CY2017	us-gaap	Proceeds From Sale And Collection Of Notes Receivable ProceedsFromSaleAndCollectionOfNotesReceivable	0	USD
CY2015	us-gaap	Profit Loss ProfitLoss	123317000	USD
CY2016Q1	us-gaap	Profit Loss ProfitLoss	57665000	USD
CY2016Q2	us-gaap	Profit Loss ProfitLoss	27287000	USD
CY2016Q3	us-gaap	Profit Loss ProfitLoss	12261000	USD
CY2016Q4	us-gaap	Profit Loss ProfitLoss	40103000	USD
CY2016	us-gaap	Profit Loss ProfitLoss	137316000	USD
CY2017Q1	us-gaap	Profit Loss ProfitLoss	62137000	USD
CY2017Q2	us-gaap	Profit Loss ProfitLoss	21722000	USD
CY2017Q3	us-gaap	Profit Loss ProfitLoss	4458000	USD
CY2017Q4	us-gaap	Profit Loss ProfitLoss	27615000	USD
CY2017	us-gaap	Profit Loss ProfitLoss	115932000	USD
CY2016Q4	us-gaap	Property Plant And Equipment Gross PropertyPlantAndEquipmentGross	5656973000	USD
CY2017Q4	us-gaap	Property Plant And Equipment Gross PropertyPlantAndEquipmentGross	6011147000	USD
CY2015	us-gaap	Public Utilities Allowance For Funds Used During Construction Additions PublicUtilitiesAllowanceForFundsUsedDuringConstructionAdditions	3546000	USD
CY2016	us-gaap	Public Utilities Allowance For Funds Used During Construction Additions PublicUtilitiesAllowanceForFundsUsedDuringConstructionAdditions	2651000	USD
CY2017	us-gaap	Public Utilities Allowance For Funds Used During Construction Additions PublicUtilitiesAllowanceForFundsUsedDuringConstructionAdditions	3310000	USD
CY2015	us-gaap	Public Utilities Allowance For Funds Used During Construction Capitalized Cost Of Equity PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity	8331000	USD
CY2016	us-gaap	Public Utilities Allowance For Funds Used During Construction Capitalized Cost Of Equity PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity	8475000	USD
CY2017	us-gaap	Public Utilities Allowance For Funds Used During Construction Capitalized Cost Of Equity PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity	6669000	USD
CY2016Q4	us-gaap	Public Utilities Property Plant And Equipment Accumulated Depreciation PublicUtilitiesPropertyPlantAndEquipmentAccumulatedDepreciation	1509473000	USD
CY2017Q4	us-gaap	Public Utilities Property Plant And Equipment Accumulated Depreciation PublicUtilitiesPropertyPlantAndEquipmentAccumulatedDepreciation	1612337000	USD
CY2016Q4	us-gaap	Public Utilities Property Plant And Equipment Construction Work In Progress PublicUtilitiesPropertyPlantAndEquipmentConstructionWorkInProgress	150474000	USD
CY2016	us-gaap	Real Estate Tax Expense RealEstateTaxExpense	38505000	USD
CY2017	us-gaap	Real Estate Tax Expense RealEstateTaxExpense	40074000	USD
CY2016Q4	us-gaap	Refundable Gas Costs RefundableGasCosts	30800000	USD
CY2016Q4	us-gaap	Refundable Gas Costs RefundableGasCosts	30820000	USD
CY2017Q4	us-gaap	Refundable Gas Costs RefundableGasCosts	37474000	USD
CY2017Q4	us-gaap	Refundable Gas Costs RefundableGasCosts	37500000	USD
CY2016Q4	us-gaap	Regulated Entity Other Assets Noncurrent RegulatedEntityOtherAssetsNoncurrent	669471000	USD
CY2017Q4	us-gaap	Regulated Entity Other Assets Noncurrent RegulatedEntityOtherAssetsNoncurrent	625257000	USD
CY2017	us-gaap	Revenues Revenues	1445929000	USD
CY2016Q4	us-gaap	Secured Debt SecuredDebt	1696700000	USD
CY2017Q4	us-gaap	Secured Debt SecuredDebt	1786700000	USD
CY2015	us-gaap	Share Based Compensation ShareBasedCompensation	6914000	USD
CY2016	us-gaap	Share Based Compensation ShareBasedCompensation	7891000	USD
CY2017	us-gaap	Share Based Compensation ShareBasedCompensation	7359000	USD
CY2016Q4	us-gaap	Short Term Borrowings ShortTermBorrowings	120000000	USD
CY2017Q4	us-gaap	Short Term Borrowings ShortTermBorrowings	105398000	USD
CY2016Q4	us-gaap	Regulatory Assets RegulatoryAssets	699828000	USD
CY2017Q4	us-gaap	Regulatory Assets RegulatoryAssets	664149000	USD
CY2016Q4	us-gaap	Regulatory Assets Noncurrent RegulatoryAssetsNoncurrent	135751000	USD
CY2017Q4	us-gaap	Regulatory Assets Noncurrent RegulatoryAssetsNoncurrent	127328000	USD
CY2016Q4	us-gaap	Regulatory Liabilities RegulatoryLiabilities	396952000	USD
CY2017Q4	us-gaap	Regulatory Liabilities RegulatoryLiabilities	848353000	USD
CY2017Q4	us-gaap	Remaining Amounts Of Regulatory Assets For Which No Return On Investment During Recovery Period Is Provided RemainingAmountsOfRegulatoryAssetsForWhichNoReturnOnInvestmentDuringRecoveryPeriodIsProvided	284757000	USD
CY2015	us-gaap	Repayments Of Long Term Debt RepaymentsOfLongTermDebt	2905000	USD
CY2016	us-gaap	Repayments Of Long Term Debt RepaymentsOfLongTermDebt	163167000	USD
CY2017	us-gaap	Repayments Of Long Term Debt RepaymentsOfLongTermDebt	3287000	USD
CY2015	us-gaap	Repayments Of Other Debt RepaymentsOfOtherDebt	1431000	USD
CY2016	us-gaap	Repayments Of Other Debt RepaymentsOfOtherDebt	0	USD
CY2017	us-gaap	Repayments Of Other Debt RepaymentsOfOtherDebt	0	USD
CY2016Q4	us-gaap	Retained Earnings Accumulated Deficit RetainedEarningsAccumulatedDeficit	581014000	USD
CY2017Q4	us-gaap	Retained Earnings Accumulated Deficit RetainedEarningsAccumulatedDeficit	604470000	USD
CY2016Q4	us-gaap	Retained Earnings Appropriated RetainedEarningsAppropriated	25564000	USD
CY2017Q4	us-gaap	Retained Earnings Appropriated RetainedEarningsAppropriated	33917000	USD
CY2015	us-gaap	Revenues Revenues	1484776000	USD
CY2016Q1	us-gaap	Revenues Revenues	418173000	USD
CY2016Q2	us-gaap	Revenues Revenues	318838000	USD
CY2016Q3	us-gaap	Revenues Revenues	303349000	USD
CY2016Q4	us-gaap	Revenues Revenues	402123000	USD
CY2016	us-gaap	Revenues Revenues	1442483000	USD
CY2017Q1	us-gaap	Revenues Revenues	436470000	USD
CY2017Q2	us-gaap	Revenues Revenues	314501000	USD
CY2017Q3	us-gaap	Revenues Revenues	297096000	USD
CY2017Q4	us-gaap	Revenues Revenues	397862000	USD
CY2015Q4	us-gaap	Stockholders Equity StockholdersEquity	1528626000	USD
CY2016Q4	us-gaap	Stockholders Equity StockholdersEquity	1648727000	USD
CY2017Q4	us-gaap	Stockholders Equity StockholdersEquity	1729828000	USD
CY2015Q4	us-gaap	Stockholders Equity Including Portion Attributable To Noncontrolling Interest StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	1528287000	USD
CY2016Q4	us-gaap	Stockholders Equity Including Portion Attributable To Noncontrolling Interest StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	1648476000	USD
CY2017Q4	us-gaap	Stockholders Equity Including Portion Attributable To Noncontrolling Interest StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	1730484000	USD
CY2015	us-gaap	Treasury Stock Acquired Average Cost Per Share TreasuryStockAcquiredAverageCostPerShare	32.66
CY2016Q4	us-gaap	Unamortized Debt Issuance Expense UnamortizedDebtIssuanceExpense	10639000	USD
CY2017Q4	us-gaap	Unamortized Debt Issuance Expense UnamortizedDebtIssuanceExpense	10285000	USD
CY2016Q4	us-gaap	Unbilled Receivables Current UnbilledReceivablesCurrent	72377000	USD
CY2017Q4	us-gaap	Unbilled Receivables Current UnbilledReceivablesCurrent	68641000	USD
CY2015	us-gaap	Unrecognized Tax Benefits Income Tax Penalties And Interest Expense UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense	0	USD
CY2016	us-gaap	Unrecognized Tax Benefits Income Tax Penalties And Interest Expense UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense	0	USD
CY2016Q1	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	62907000	shares
CY2016Q2	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	63783000	shares
CY2016Q3	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	64325000	shares
CY2016Q4	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	64620000	shares
CY2016	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	63920000	shares
CY2017Q2	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	64553000	shares
CY2017Q3	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	64892000	shares
CY2017Q4	us-gaap	Unrecorded Unconditional Purchase Obligation Balance On Fifth Anniversary UnrecordedUnconditionalPurchaseObligationBalanceOnFifthAnniversary	179001000	USD
CY2017Q4	us-gaap	Unrecorded Unconditional Purchase Obligation Balance On First Anniversary UnrecordedUnconditionalPurchaseObligationBalanceOnFirstAnniversary	267198000	USD
CY2017Q4	us-gaap	Unrecorded Unconditional Purchase Obligation Balance On Fourth Anniversary UnrecordedUnconditionalPurchaseObligationBalanceOnFourthAnniversary	180553000	USD
CY2017Q4	us-gaap	Unrecorded Unconditional Purchase Obligation Balance On Second Anniversary UnrecordedUnconditionalPurchaseObligationBalanceOnSecondAnniversary	246552000	USD
CY2017Q4	us-gaap	Unrecorded Unconditional Purchase Obligation Balance On Third Anniversary UnrecordedUnconditionalPurchaseObligationBalanceOnThirdAnniversary	209694000	USD
CY2017Q4	us-gaap	Unrecorded Unconditional Purchase Obligation Balance Sheet Amount UnrecordedUnconditionalPurchaseObligationBalanceSheetAmount	2325735000	USD
CY2017Q4	us-gaap	Unrecorded Unconditional Purchase Obligation Due After Five Years UnrecordedUnconditionalPurchaseObligationDueAfterFiveYears	1242737000	USD
CY2015	us-gaap	Utilities Operating Expense Depreciation And Amortization UtilitiesOperatingExpenseDepreciationAndAmortization	143499000	USD
CY2016	us-gaap	Utilities Operating Expense Depreciation And Amortization UtilitiesOperatingExpenseDepreciationAndAmortization	160514000	USD
CY2017	us-gaap	Utilities Operating Expense Depreciation And Amortization UtilitiesOperatingExpenseDepreciationAndAmortization	171281000	USD
CY2015	us-gaap	Utilities Operating Expense Maintenance Operations And Other Costs And Expenses UtilitiesOperatingExpenseMaintenanceOperationsAndOtherCostsAndExpenses	303221000	USD
CY2016	us-gaap	Utilities Operating Expense Maintenance Operations And Other Costs And Expenses UtilitiesOperatingExpenseMaintenanceOperationsAndOtherCostsAndExpenses	315795000	USD
CY2017	us-gaap	Utilities Operating Expense Maintenance Operations And Other Costs And Expenses UtilitiesOperatingExpenseMaintenanceOperationsAndOtherCostsAndExpenses	317813000	USD
CY2015	us-gaap	Utilities Operating Expense Products And Services UtilitiesOperatingExpenseProductsAndServices	656964000	USD
CY2016	us-gaap	Utilities Operating Expense Products And Services UtilitiesOperatingExpenseProductsAndServices	551366000	USD
CY2017	us-gaap	Utilities Operating Expense Products And Services UtilitiesOperatingExpenseProductsAndServices	524566000	USD
CY2015	us-gaap	Utilities Operating Expense Taxes UtilitiesOperatingExpenseTaxes	97657000	USD
CY2016	us-gaap	Utilities Operating Expense Taxes UtilitiesOperatingExpenseTaxes	98735000	USD
CY2017	us-gaap	Utilities Operating Expense Taxes UtilitiesOperatingExpenseTaxes	106752000	USD
CY2015	us-gaap	Utility Revenue UtilityRevenue	1456091000	USD
CY2016	us-gaap	Utility Revenue UtilityRevenue	1418914000	USD
CY2017	us-gaap	Utility Revenue UtilityRevenue	1423386000	USD
CY2015	us-gaap	Valuation Allowances And Reserves Charged To Cost And Expense ValuationAllowancesAndReservesChargedToCostAndExpense	5802000	USD
CY2016	us-gaap	Valuation Allowances And Reserves Charged To Cost And Expense ValuationAllowancesAndReservesChargedToCostAndExpense	6053000	USD
CY2017	us-gaap	Valuation Allowances And Reserves Charged To Cost And Expense ValuationAllowancesAndReservesChargedToCostAndExpense	5317000	USD
CY2015	us-gaap	Valuation Allowances And Reserves Deductions ValuationAllowancesAndReservesDeductions	6160000	USD
CY2016	us-gaap	Valuation Allowances And Reserves Deductions ValuationAllowancesAndReservesDeductions	5557000	USD
CY2017	us-gaap	Valuation Allowances And Reserves Deductions ValuationAllowancesAndReservesDeductions	5211000	USD
CY2015	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	62708000	shares
CY2017Q1	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	64469000	shares
CY2017Q4	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	65308000	shares
CY2017	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	64806000	shares
CY2015	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	62301000	shares
CY2016Q1	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	62605000	shares
CY2016Q2	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	63386000	shares
CY2016Q3	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	63857000	shares
CY2016Q4	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	64185000	shares
CY2016	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	63508000	shares
CY2017Q1	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	64362000	shares
CY2017Q2	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	64401000	shares
CY2017Q3	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	64412000	shares
CY2017Q4	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	64809000	shares
CY2017	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	64496000	shares
CY2017	us-gaap	Derivatives Reporting Of Derivative Activity DerivativesReportingOfDerivativeActivity	<div style="font-family:Times New Roman;font-size:10pt;"><div style="line-height:120%;padding-top:12px;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;font-style:italic;font-weight:bold;">Derivative Assets and Liabilities</font></div><div style="line-height:120%;padding-top:6px;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;">Derivatives are recorded as either assets or liabilities on the Consolidated Balance Sheets measured at estimated fair value.</font></div><div style="line-height:120%;padding-top:8px;text-align:left;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;">The WUTC and the IPUC issued accounting orders authorizing Avista Corp. to offset energy commodity derivative assets or liabilities with a regulatory asset or liability. This accounting treatment is intended to defer the recognition of mark-to-market gains and losses on energy commodity transactions until the period of delivery. Realized benefits and costs result in adjustments to retail rates through PGAs, the ERM in Washington, the PCA mechanism in Idaho, and periodic general rates cases. The resulting regulatory assets have been concluded to be probable of recovery through future rates.</font></div><div style="line-height:120%;padding-top:12px;text-align:left;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;">Substantially all forward contracts to purchase or sell power and natural gas are recorded as derivative assets or liabilities at estimated fair value with an offsetting regulatory asset or liability. Contracts that are not considered derivatives are accounted for on the accrual basis until they are settled or realized unless there is a decline in the fair value of the contract that is determined to be other-than-temporary.</font></div><div style="line-height:120%;padding-top:8px;text-align:left;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;">For interest rate swap derivatives, Avista Corp. records all mark-to-market gains and losses in each accounting period as assets and liabilities, as well as offsetting regulatory assets and liabilities, such that there is no income statement impact. The interest rate swap derivatives are risk management tools similar to energy commodity derivatives. Upon settlement of interest rate swap derivatives, the regulatory asset or liability is amortized as a component of interest expense over the term of the associated debt. The Company records an offset of interest rate swap derivative assets and liabilities with regulatory assets and liabilities, based on the prior practice of the commissions to provide recovery through the ratemaking process. See Note 19 for additional discussion regarding interest rate swaps in the Company's 2017 Washington general rate cases.</font></div><div style="line-height:120%;padding-top:12px;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;">As of </font><font style="font-family:inherit;font-size:10pt;">December 31, 2017</font><font style="font-family:inherit;font-size:10pt;">, the Company has multiple master netting agreements with a variety of entities that allow for cross-commodity netting of derivative agreements with the same counterparty (i.e. power derivatives can be netted with natural gas derivatives). In addition, some master netting agreements allow for the netting of commodity derivatives and interest rate swap derivatives for the same counterparty. The Company does not have any agreements which allow for cross-affiliate netting among multiple affiliated legal entities. The Company nets all derivative instruments when allowed by the agreement for presentation in the Consolidated Balance Sheets.</font></div></div>
CY2017	us-gaap	Nature Of Operations NatureOfOperations	<div style="font-family:Times New Roman;font-size:10pt;"><div style="line-height:120%;padding-top:6px;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;font-style:italic;font-weight:bold;">Nature of Business</font></div><div style="line-height:120%;padding-top:6px;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;">Avista Corp. is primarily an electric and natural gas utility with certain other business ventures. Avista Utilities is an operating division of Avista Corp., comprising the regulated utility operations in the Pacific Northwest. Avista Utilities provides electric distribution and transmission, and natural gas distribution services in parts of eastern Washington and northern Idaho. Avista Utilities also provides natural gas distribution service in parts of northeastern and southwestern Oregon. Avista Utilities has electric generating facilities in Washington, Idaho, Oregon and Montana. Avista Utilities also supplies electricity to a small number of customers in Montana, most of whom are employees who operate Avista Utilities' Noxon Rapids generating facility.</font></div><div style="line-height:120%;padding-top:6px;text-align:left;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;">AERC is a wholly-owned subsidiary of Avista Corp. The primary subsidiary of AERC is AEL&P, which comprises Avista Corp.'s regulated utility operations in Alaska.</font></div><div style="line-height:120%;padding-top:6px;text-align:left;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;">Avista Capital, a wholly owned non-regulated subsidiary of Avista Corp., is the parent company of all of the subsidiary companies in the non-utility businesses, with the exception of AJT Mining Properties, which is a subsidiary of AERC. See Note 21 for business segment information.</font></div><div style="line-height:120%;padding-top:6px;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;">On July 19, 2017, Avista Corp. entered into an Agreement and Plan of Merger (Merger Agreement) to become a wholly-owned subsidiary of Hydro One. Consummation of the pending acquisition is subject to a number of approvals and the satisfaction or waiver of other specified conditions. The transaction is expected to close in the second half of 2018. See Note 4 for additional information.</font></div><div style="line-height:120%;padding-top:12px;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;font-style:italic;font-weight:bold;"></font></div></div>
CY2017	us-gaap	Use Of Estimates UseOfEstimates	<div style="font-family:Times New Roman;font-size:10pt;"><div style="line-height:120%;padding-top:12px;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;font-style:italic;font-weight:bold;">Use of Estimates</font></div><div style="line-height:120%;padding-top:6px;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;">The preparation of the consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported for assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Significant estimates include:</font></div><table cellpadding="0" cellspacing="0" style="padding-top:8px;font-family:Times New Roman; font-size:10pt;"><tr><td style="width:96px;" rowspan="1" colspan="1"></td><td rowspan="1" colspan="1"></td></tr><tr><td style="vertical-align:top" rowspan="1" colspan="1"><div style="line-height:120%;font-size:10pt;padding-left:48px;"><font style="font-family:inherit;font-size:10pt;">•</font></div></td><td style="vertical-align:top;" rowspan="1" colspan="1"><div style="line-height:120%;text-align:left;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;">determining the market value of energy commodity derivative assets and liabilities,</font></div></td></tr></table><table cellpadding="0" cellspacing="0" style="padding-top:8px;font-family:Times New Roman; font-size:10pt;"><tr><td style="width:96px;" rowspan="1" colspan="1"></td><td rowspan="1" colspan="1"></td></tr><tr><td style="vertical-align:top" rowspan="1" colspan="1"><div style="line-height:120%;font-size:10pt;padding-left:48px;"><font style="font-family:inherit;font-size:10pt;">•</font></div></td><td style="vertical-align:top;" rowspan="1" colspan="1"><div style="line-height:120%;text-align:left;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;">pension and other postretirement benefit plan obligations,</font></div></td></tr></table><table cellpadding="0" cellspacing="0" style="padding-top:8px;font-family:Times New Roman; font-size:10pt;"><tr><td style="width:96px;" rowspan="1" colspan="1"></td><td rowspan="1" colspan="1"></td></tr><tr><td style="vertical-align:top" rowspan="1" colspan="1"><div style="line-height:120%;font-size:10pt;padding-left:48px;"><font style="font-family:inherit;font-size:10pt;">•</font></div></td><td style="vertical-align:top;" rowspan="1" colspan="1"><div style="line-height:120%;text-align:left;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;">contingent liabilities,</font></div></td></tr></table><table cellpadding="0" cellspacing="0" style="padding-top:8px;font-family:Times New Roman; font-size:10pt;"><tr><td style="width:96px;" rowspan="1" colspan="1"></td><td rowspan="1" colspan="1"></td></tr><tr><td style="vertical-align:top" rowspan="1" colspan="1"><div style="line-height:120%;font-size:10pt;padding-left:48px;"><font style="font-family:inherit;font-size:10pt;">•</font></div></td><td style="vertical-align:top;" rowspan="1" colspan="1"><div style="line-height:120%;text-align:left;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;">goodwill impairment testing,</font></div></td></tr></table><table cellpadding="0" cellspacing="0" style="padding-top:8px;font-family:Times New Roman; font-size:10pt;"><tr><td style="width:96px;" rowspan="1" colspan="1"></td><td rowspan="1" colspan="1"></td></tr><tr><td style="vertical-align:top" rowspan="1" colspan="1"><div style="line-height:120%;font-size:10pt;padding-left:48px;"><font style="font-family:inherit;font-size:10pt;">•</font></div></td><td style="vertical-align:top;" rowspan="1" colspan="1"><div style="line-height:120%;text-align:left;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;">recoverability of regulatory assets, and</font></div></td></tr></table><table cellpadding="0" cellspacing="0" style="padding-top:8px;font-family:Times New Roman; font-size:10pt;"><tr><td style="width:96px;" rowspan="1" colspan="1"></td><td rowspan="1" colspan="1"></td></tr><tr><td style="vertical-align:top" rowspan="1" colspan="1"><div style="line-height:120%;font-size:10pt;padding-left:48px;"><font style="font-family:inherit;font-size:10pt;">•</font></div></td><td style="vertical-align:top;" rowspan="1" colspan="1"><div style="line-height:120%;text-align:left;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;">unbilled revenues.</font></div></td></tr></table><div style="line-height:120%;padding-top:12px;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;">Changes in these estimates and assumptions are considered reasonably possible and may have a material effect on the consolidated financial statements and thus actual results could differ from the amounts reported and disclosed herein.</font></div></div>

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$AVA
AVISTA CORP Stock $ava

2017 Form 10-K Financial Statement

#000010491818000043 Filed on February 21, 2018

Income Statement

Balance Sheet

Cashflow Statement

Facts In Submission

Files In Submission

$AVA AVISTA CORP Stock $ava

2017 Form 10-K Financial Statement

#000010491818000043 Filed on February 21, 2018

Income Statement

Balance Sheet

Cashflow Statement

Facts In Submission

Files In Submission

$AVA
AVISTA CORP Stock $ava