$FSLY
Fastly Inc Stock $fsly

$fsly Overview Financials Valuation SEC Filings Company Website

2019 Q4 Form 10-K Financial Statement

#000151741321000030 Filed on March 01, 2021

Income Statement

Concept	2019 Q4	2018 Q4	2018
Revenue	$58.94M	$40.80M	$144.6M
YoY Change	44.46%	35.82%	37.81%
Cost Of Revenue	$25.53M	$17.71M	$65.50M
YoY Change	44.16%	22.22%	34.57%
Gross Profit	$33.41M	$23.09M	$79.06M
YoY Change	44.69%	48.58%	40.61%
Gross Profit Margin	56.68%	56.59%	54.69%
Selling, General & Admin	$34.49M	$20.84M	$73.58M
YoY Change	65.5%	24.57%	26.28%
% of Gross Profit	103.23%	90.26%	93.07%
Research & Development	$12.95M	$9.310M	$34.62M
YoY Change	39.1%	17.7%	19.42%
% of Gross Profit	38.76%	40.32%	43.78%
Depreciation & Amortization	$4.860M	$3.680M	$13.40M
YoY Change	32.07%		38.98%
% of Gross Profit	14.55%	15.94%	16.95%
Operating Expenses	$47.44M	$30.15M	$108.2M
YoY Change	57.35%	22.36%	24.0%
Operating Profit	-$14.03M	-$7.060M	-$29.14M
YoY Change	98.73%	-22.42%	-6.1%
Interest Expense	$470.0K	-$230.0K	$1.810M
YoY Change	-304.35%	15.0%	62.19%
% of Operating Profit
Other Income/Expense, Net	-$200.0K	$20.00K	-$741.0K
YoY Change	-1100.0%	-128.57%	37.48%
Pretax Income	-$13.76M	-$7.270M	-$20.64M
YoY Change	89.27%	-22.33%	-11.67%
Income Tax	$310.0K	$40.00K	$185.0K
% Of Pretax Income
Net Earnings	-$14.07M	-$7.310M	-$30.94M
YoY Change	92.48%	-22.32%	-4.67%
Net Earnings / Revenue	-23.87%	-17.92%	-21.4%
Basic Earnings Per Share
Diluted Earnings Per Share	-$149.1K	-$80.60K	-$340.7K
COMMON SHARES
Basic Shares Outstanding
Diluted Shares Outstanding

Balance Sheet

Concept	2019 Q4	2018 Q4	2018
SHORT-TERM ASSETS
Cash & Short-Term Investments	$131.1M	$83.64M	$83.60M
YoY Change	56.75%		66.53%
Cash & Equivalents	$16.14M	$36.96M	$2.400M
Short-Term Investments	$115.0M	$46.68M	$48.70M
Other Short-Term Assets	$81.10M		$8.900M
YoY Change			32.84%
Inventory
Prepaid Expenses
Receivables	$37.14M	$24.73M	$24.70M
Other Receivables	$0.00		$0.00
Total Short-Term Assets	$249.3M	$117.3M	$117.3M
YoY Change	112.61%		54.55%
LONG-TERM ASSETS
Property, Plant & Equipment	$60.04M	$42.35M	$42.40M
YoY Change	41.75%		14.59%
Goodwill	$372.0K	$360.0K
YoY Change	3.33%	-5.76%
Intangibles	$1.125M	$610.0K
YoY Change	84.43%
Long-Term Investments
YoY Change
Other Assets	$10.11M	$2.163M	$2.200M
YoY Change	367.5%		0.0%
Total Long-Term Assets	$71.65M	$45.49M	$45.50M
YoY Change	57.51%		12.9%
TOTAL ASSETS
Total Short-Term Assets	$249.3M	$117.3M	$117.3M
Total Long-Term Assets	$71.65M	$45.49M	$45.50M
Total Assets	$321.0M	$162.8M	$162.8M
YoY Change	97.21%		40.1%
SHORT-TERM LIABILITIES
YoY Change
Accounts Payable	$4.602M	$2.333M	$2.300M
YoY Change	97.26%		-43.9%
Accrued Expenses	$19.88M	$15.54M	$12.50M
YoY Change	27.96%		31.58%
Deferred Revenue	$317.0K	$1.622M
YoY Change	-80.46%
Short-Term Debt	$0.00		$0.00
YoY Change
Long-Term Debt Due	$4.472M	$11.37M	$11.40M
YoY Change	-60.67%		533.33%
Total Short-Term Liabilities	$37.12M	$31.75M	$31.80M
YoY Change	16.92%		74.73%
LONG-TERM LIABILITIES
Long-Term Debt	$20.08M	$39.44M	$39.40M
YoY Change	-49.08%		69.83%
Other Long-Term Liabilities	$1.038M	$647.0K	$3.900M
YoY Change	60.43%		85.71%
Total Long-Term Liabilities	$21.12M	$40.09M	$43.30M
YoY Change	-47.32%		71.15%
TOTAL LIABILITIES
Total Short-Term Liabilities	$37.12M	$31.75M	$31.80M
Total Long-Term Liabilities	$21.12M	$40.09M	$43.30M
Total Liabilities	$63.32M	$75.10M	$75.10M
YoY Change	-15.69%		72.64%
SHAREHOLDERS EQUITY
Retained Earnings	-$192.0M	-$146.2M
YoY Change	31.35%
Common Stock	$2.000K	$1.000K
YoY Change	100.0%
Preferred Stock
YoY Change
Treasury Stock (at cost)	$0.00	$2.109M
YoY Change	-100.0%
Treasury Stock Shares
Shareholders Equity	$257.7M	-$131.9M	$87.70M
YoY Change
Total Liabilities & Shareholders Equity	$321.0M	$162.8M	$162.8M
YoY Change	97.21%		40.1%

Cashflow Statement

Concept	2019 Q4	2018 Q4	2018
OPERATING ACTIVITIES
Net Income	-$14.07M	-$7.310M	-$30.94M
YoY Change	92.48%	-22.32%	-4.67%
Depreciation, Depletion And Amortization	$4.860M	$3.680M	$13.40M
YoY Change	32.07%		38.98%
Cash From Operating Activities	-$3.060M	-$790.0K	-$16.99M
YoY Change	287.34%		-34.32%
INVESTING ACTIVITIES
Capital Expenditures	-$5.850M	-$7.330M	$16.70M
YoY Change	-20.19%		38.04%
Acquisitions			$0.00
YoY Change
Other Investing Activities	$38.32M	-$1.430M	-$27.36M
YoY Change	-2779.72%		981.42%
Cash From Investing Activities	$32.48M	-$8.760M	-$47.11M
YoY Change	-470.78%		198.52%
FINANCING ACTIVITIES
Cash Dividend Paid
YoY Change
Common Stock Issuance & Retirement, Net			$0.00
YoY Change
Debt Paid & Issued, Net
YoY Change
Cash From Financing Activities	1.930M	25.31M	$69.64M
YoY Change	-92.37%		25.68%
NET CHANGE
Cash From Operating Activities	-3.060M	-790.0K	-$16.99M
Cash From Investing Activities	32.48M	-8.760M	-$47.11M
Cash From Financing Activities	1.930M	25.31M	$69.64M
Net Change In Cash	31.35M	15.76M	$5.567M
YoY Change	98.92%		-59.46%
FREE CASH FLOW
Cash From Operating Activities	-$3.060M	-$790.0K	-$16.99M
Capital Expenditures	-$5.850M	-$7.330M	$16.70M
Free Cash Flow	$2.790M	$6.540M	-$33.69M
YoY Change	-57.34%		-11.26%

Facts In Submission

Frame	Concept Type	Concept / XBRL Key	Value	Unit
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CY2020	dei	Document Fiscal Year Focus DocumentFiscalYearFocus	2020
CY2020	dei	Document Fiscal Period Focus DocumentFiscalPeriodFocus	FY
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CY2020	dei	Document Type DocumentType	10-K
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CY2020	dei	Document Period End Date DocumentPeriodEndDate	2020-12-31
CY2020	dei	Current Fiscal Year End Date CurrentFiscalYearEndDate	--12-31
CY2020	dei	Document Transition Report DocumentTransitionReport	false
CY2020	dei	Entity File Number EntityFileNumber	001-38897
CY2020	dei	Entity Registrant Name EntityRegistrantName	FASTLY, INC.
CY2020	dei	Entity Incorporation State Country Code EntityIncorporationStateCountryCode	DE
CY2020	dei	Entity Tax Identification Number EntityTaxIdentificationNumber	27-5411834
CY2020	dei	Entity Address Address Line1 EntityAddressAddressLine1	475 Brannan Street, Suite 300
CY2020	dei	Entity Address City Or Town EntityAddressCityOrTown	San Francisco
CY2020	dei	Entity Address State Or Province EntityAddressStateOrProvince	CA
CY2020	dei	Entity Address Postal Zip Code EntityAddressPostalZipCode	94107
CY2020	dei	City Area Code CityAreaCode	844
CY2020	dei	Local Phone Number LocalPhoneNumber	432-7859
CY2020	dei	Security12b Title Security12bTitle	Class A Common Stock, $0.00002 par value
CY2020	dei	Trading Symbol TradingSymbol	FSLY
CY2020	dei	Security Exchange Name SecurityExchangeName	NYSE
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CY2020	dei	Entity Voluntary Filers EntityVoluntaryFilers	No
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CY2020	dei	Entity Interactive Data Current EntityInteractiveDataCurrent	Yes
CY2020	dei	Entity Filer Category EntityFilerCategory	Large Accelerated Filer
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CY2019	us-gaap	Stock Issued During Period Value New Issues StockIssuedDuringPeriodValueNewIssues	186912000	USD
CY2019	us-gaap	Stock Issued During Period Value Stock Options Exercised StockIssuedDuringPeriodValueStockOptionsExercised	5579000	USD
CY2019	fsly	Stock Issued During Period Value Vesting Of Early Exercised Stock Options StockIssuedDuringPeriodValueVestingOfEarlyExercisedStockOptions	620000	USD
CY2019	us-gaap	Stock Issued During Period Value Employee Stock Purchase Plan StockIssuedDuringPeriodValueEmployeeStockPurchasePlan	4150000	USD
CY2019	us-gaap	Adjustments To Additional Paid In Capital Sharebased Compensation Requisite Service Period Recognition Value AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue	12586000	USD
CY2019	fsly	Stockholders Equity Note Repayment StockholdersEquityNoteRepayment	74000	USD
CY2019	us-gaap	Net Income Loss NetIncomeLoss	-51550000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent	232000	USD
CY2019Q4	us-gaap	Stockholders Equity StockholdersEquity	257652000	USD
CY2019Q4	us-gaap	Stockholders Equity StockholdersEquity	257652000	USD
CY2020	us-gaap	Stock Issued During Period Value New Issues StockIssuedDuringPeriodValueNewIssues	274177000	USD
CY2020	us-gaap	Stock Issued During Period Value Acquisitions StockIssuedDuringPeriodValueAcquisitions	622595000	USD
CY2020	fsly	Stock Issued During Period Value Acquisition Shares Held Back For Restricted Stock Awards StockIssuedDuringPeriodValueAcquisitionSharesHeldBackForRestrictedStockAwards	87714000	USD
CY2020	us-gaap	Stock Issued During Period Shares Restricted Stock Award Net Of Forfeitures StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures	112062	shares
CY2020	us-gaap	Stock Issued During Period Value Stock Options Exercised StockIssuedDuringPeriodValueStockOptionsExercised	15273000	USD
CY2020	fsly	Stock Issued During Period Value Vesting Of Early Exercised Stock Options StockIssuedDuringPeriodValueVestingOfEarlyExercisedStockOptions	467000	USD
CY2020	us-gaap	Stock Issued During Period Value Employee Stock Purchase Plan StockIssuedDuringPeriodValueEmployeeStockPurchasePlan	8193000	USD
CY2020	us-gaap	Adjustments To Additional Paid In Capital Sharebased Compensation Requisite Service Period Recognition Value AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue	66467000	USD
CY2020	us-gaap	Net Income Loss NetIncomeLoss	-95932000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent	-190000	USD
CY2020Q4	us-gaap	Stockholders Equity StockholdersEquity	1061865000	USD
CY2020	us-gaap	Net Income Loss NetIncomeLoss	-95932000	USD
CY2019	us-gaap	Net Income Loss NetIncomeLoss	-51550000	USD
CY2018	us-gaap	Net Income Loss NetIncomeLoss	-30935000	USD
CY2020	us-gaap	Depreciation Depletion And Amortization DepreciationDepletionAndAmortization	19979000	USD
CY2019	us-gaap	Depreciation Depletion And Amortization DepreciationDepletionAndAmortization	16553000	USD
CY2018	us-gaap	Depreciation Depletion And Amortization DepreciationDepletionAndAmortization	13400000	USD
CY2020	fsly	Amortization Of Intangible Assets Acquired AmortizationOfIntangibleAssetsAcquired	5078000	USD
CY2019	fsly	Amortization Of Intangible Assets Acquired AmortizationOfIntangibleAssetsAcquired	0	USD
CY2018	fsly	Amortization Of Intangible Assets Acquired AmortizationOfIntangibleAssetsAcquired	0	USD
CY2020	fsly	Amortization Of Right Of Use Assets And Other AmortizationOfRightOfUseAssetsAndOther	21765000	USD
CY2019	fsly	Amortization Of Right Of Use Assets And Other AmortizationOfRightOfUseAssetsAndOther	0	USD
CY2018	fsly	Amortization Of Right Of Use Assets And Other AmortizationOfRightOfUseAssetsAndOther	0	USD
CY2020	fsly	Amortization Of Deferred Rent AmortizationOfDeferredRent	0	USD
CY2019	fsly	Amortization Of Deferred Rent AmortizationOfDeferredRent	-711000	USD
CY2018	fsly	Amortization Of Deferred Rent AmortizationOfDeferredRent	-340000	USD
CY2020	us-gaap	Amortization Of Financing Costs AmortizationOfFinancingCosts	219000	USD
CY2019	us-gaap	Amortization Of Financing Costs AmortizationOfFinancingCosts	1909000	USD
CY2018	us-gaap	Amortization Of Financing Costs AmortizationOfFinancingCosts	0	USD
CY2020	us-gaap	Capitalized Contract Cost Amortization CapitalizedContractCostAmortization	3516000	USD
CY2019	us-gaap	Capitalized Contract Cost Amortization CapitalizedContractCostAmortization	2294000	USD
CY2018	us-gaap	Capitalized Contract Cost Amortization CapitalizedContractCostAmortization	0	USD
CY2020	us-gaap	Share Based Compensation ShareBasedCompensation	64433000	USD
CY2019	us-gaap	Share Based Compensation ShareBasedCompensation	12145000	USD
CY2018	us-gaap	Share Based Compensation ShareBasedCompensation	4079000	USD
CY2020	us-gaap	Provision For Doubtful Accounts ProvisionForDoubtfulAccounts	1719000	USD
CY2019	us-gaap	Provision For Doubtful Accounts ProvisionForDoubtfulAccounts	360000	USD
CY2018	us-gaap	Provision For Doubtful Accounts ProvisionForDoubtfulAccounts	599000	USD
CY2020	us-gaap	Fair Value Adjustment Of Warrants FairValueAdjustmentOfWarrants	0	USD
CY2019	us-gaap	Fair Value Adjustment Of Warrants FairValueAdjustmentOfWarrants	2404000	USD
CY2018	us-gaap	Fair Value Adjustment Of Warrants FairValueAdjustmentOfWarrants	606000	USD
CY2020	us-gaap	Other Noncash Income Expense OtherNoncashIncomeExpense	-624000	USD
CY2019	us-gaap	Other Noncash Income Expense OtherNoncashIncomeExpense	591000	USD
CY2018	us-gaap	Other Noncash Income Expense OtherNoncashIncomeExpense	354000	USD
CY2020	fsly	Interest Paid On Capital Lease InterestPaidOnCapitalLease	688000	USD
CY2019	fsly	Interest Paid On Capital Lease InterestPaidOnCapitalLease	364000	USD
CY2018	fsly	Interest Paid On Capital Lease InterestPaidOnCapitalLease	203000	USD
CY2020	us-gaap	Gain Loss On Sale Of Property Plant Equipment GainLossOnSaleOfPropertyPlantEquipment	-653000	USD
CY2019	us-gaap	Gain Loss On Sale Of Property Plant Equipment GainLossOnSaleOfPropertyPlantEquipment	-108000	USD
CY2018	us-gaap	Gain Loss On Sale Of Property Plant Equipment GainLossOnSaleOfPropertyPlantEquipment	0	USD
CY2020	fsly	Tax Benefit Related To Release Of Valuation Allowance TaxBenefitRelatedToReleaseOfValuationAllowance	12950000	USD
CY2019	fsly	Tax Benefit Related To Release Of Valuation Allowance TaxBenefitRelatedToReleaseOfValuationAllowance	0	USD
CY2018	fsly	Tax Benefit Related To Release Of Valuation Allowance TaxBenefitRelatedToReleaseOfValuationAllowance	0	USD
CY2020	us-gaap	Increase Decrease In Accounts Receivable IncreaseDecreaseInAccountsReceivable	9264000	USD
CY2019	us-gaap	Increase Decrease In Accounts Receivable IncreaseDecreaseInAccountsReceivable	12767000	USD
CY2018	us-gaap	Increase Decrease In Accounts Receivable IncreaseDecreaseInAccountsReceivable	6234000	USD
CY2020	us-gaap	Increase Decrease In Prepaid Deferred Expense And Other Assets IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets	5550000	USD
CY2019	us-gaap	Increase Decrease In Prepaid Deferred Expense And Other Assets IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets	2666000	USD
CY2018	us-gaap	Increase Decrease In Prepaid Deferred Expense And Other Assets IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets	2325000	USD
CY2020	us-gaap	Increase Decrease In Other Operating Assets IncreaseDecreaseInOtherOperatingAssets	17162000	USD
CY2019	us-gaap	Increase Decrease In Other Operating Assets IncreaseDecreaseInOtherOperatingAssets	3945000	USD
CY2018	us-gaap	Increase Decrease In Other Operating Assets IncreaseDecreaseInOtherOperatingAssets	-10000	USD
CY2020	us-gaap	Increase Decrease In Accounts Payable IncreaseDecreaseInAccountsPayable	4059000	USD
CY2019	us-gaap	Increase Decrease In Accounts Payable IncreaseDecreaseInAccountsPayable	2391000	USD
CY2018	us-gaap	Increase Decrease In Accounts Payable IncreaseDecreaseInAccountsPayable	-372000	USD
CY2020	us-gaap	Increase Decrease In Accrued Liabilities IncreaseDecreaseInAccruedLiabilities	12992000	USD
CY2019	us-gaap	Increase Decrease In Accrued Liabilities IncreaseDecreaseInAccruedLiabilities	4401000	USD
CY2018	us-gaap	Increase Decrease In Accrued Liabilities IncreaseDecreaseInAccruedLiabilities	3902000	USD
CY2020	fsly	Increase Decrease In Operating Lease Liabilities IncreaseDecreaseInOperatingLeaseLiabilities	-18264000	USD
CY2019	fsly	Increase Decrease In Operating Lease Liabilities IncreaseDecreaseInOperatingLeaseLiabilities	0	USD
CY2018	fsly	Increase Decrease In Operating Lease Liabilities IncreaseDecreaseInOperatingLeaseLiabilities	0	USD
CY2020	us-gaap	Increase Decrease In Other Operating Liabilities IncreaseDecreaseInOtherOperatingLiabilities	4857000	USD
CY2019	us-gaap	Increase Decrease In Other Operating Liabilities IncreaseDecreaseInOtherOperatingLiabilities	-1274000	USD
CY2018	us-gaap	Increase Decrease In Other Operating Liabilities IncreaseDecreaseInOtherOperatingLiabilities	1182000	USD
CY2020	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	-19916000	USD
CY2019	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	-31303000	USD
CY2018	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	-16985000	USD
CY2020	us-gaap	Payments To Acquire Available For Sale Securities Debt PaymentsToAcquireAvailableForSaleSecuritiesDebt	269059000	USD
CY2019	us-gaap	Payments To Acquire Available For Sale Securities Debt PaymentsToAcquireAvailableForSaleSecuritiesDebt	190980000	USD
CY2018	us-gaap	Payments To Acquire Available For Sale Securities Debt PaymentsToAcquireAvailableForSaleSecuritiesDebt	62660000	USD
CY2020	us-gaap	Proceeds From Sale Of Available For Sale Securities Debt ProceedsFromSaleOfAvailableForSaleSecuritiesDebt	143241000	USD
CY2019	us-gaap	Proceeds From Sale Of Available For Sale Securities Debt ProceedsFromSaleOfAvailableForSaleSecuritiesDebt	52589000	USD
CY2018	us-gaap	Proceeds From Sale Of Available For Sale Securities Debt ProceedsFromSaleOfAvailableForSaleSecuritiesDebt	0	USD
CY2020	us-gaap	Proceeds From Maturities Prepayments And Calls Of Available For Sale Securities ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities	88719000	USD
CY2019	us-gaap	Proceeds From Maturities Prepayments And Calls Of Available For Sale Securities ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities	70813000	USD
CY2018	us-gaap	Proceeds From Maturities Prepayments And Calls Of Available For Sale Securities ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities	35210000	USD
CY2020	us-gaap	Payments To Acquire Businesses Net Of Cash Acquired PaymentsToAcquireBusinessesNetOfCashAcquired	200988000	USD
CY2019	us-gaap	Payments To Acquire Businesses Net Of Cash Acquired PaymentsToAcquireBusinessesNetOfCashAcquired	0	USD
CY2018	us-gaap	Payments To Acquire Businesses Net Of Cash Acquired PaymentsToAcquireBusinessesNetOfCashAcquired	0	USD
CY2020	us-gaap	Proceeds From Sale Of Property Plant And Equipment ProceedsFromSaleOfPropertyPlantAndEquipment	575000	USD
CY2019	us-gaap	Proceeds From Sale Of Property Plant And Equipment ProceedsFromSaleOfPropertyPlantAndEquipment	0	USD
CY2018	us-gaap	Proceeds From Sale Of Property Plant And Equipment ProceedsFromSaleOfPropertyPlantAndEquipment	0	USD
CY2020	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	29569000	USD
CY2019	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	14609000	USD
CY2018	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	16702000	USD
CY2020	us-gaap	Payments For Software PaymentsForSoftware	6131000	USD
CY2019	us-gaap	Payments For Software PaymentsForSoftware	4856000	USD
CY2018	us-gaap	Payments For Software PaymentsForSoftware	2955000	USD
CY2020	us-gaap	Payments To Acquire Intangible Assets PaymentsToAcquireIntangibleAssets	1811000	USD
CY2019	us-gaap	Payments To Acquire Intangible Assets PaymentsToAcquireIntangibleAssets	635000	USD
CY2018	us-gaap	Payments To Acquire Intangible Assets PaymentsToAcquireIntangibleAssets	0	USD
CY2020	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-275023000	USD
CY2019	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-87678000	USD
CY2018	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-47107000	USD
CY2020	us-gaap	Proceeds From Issuance Initial Public Offering ProceedsFromIssuanceInitialPublicOffering	0	USD
CY2019	us-gaap	Proceeds From Issuance Initial Public Offering ProceedsFromIssuanceInitialPublicOffering	192510000	USD
CY2018	us-gaap	Proceeds From Issuance Initial Public Offering ProceedsFromIssuanceInitialPublicOffering	0	USD
CY2020	us-gaap	Proceeds From Issuance Of Common Stock ProceedsFromIssuanceOfCommonStock	274896000	USD
CY2019	us-gaap	Proceeds From Issuance Of Common Stock ProceedsFromIssuanceOfCommonStock	0	USD
CY2018	us-gaap	Proceeds From Issuance Of Common Stock ProceedsFromIssuanceOfCommonStock	0	USD
CY2020	us-gaap	Proceeds From Notes Payable ProceedsFromNotesPayable	0	USD
CY2019	us-gaap	Proceeds From Notes Payable ProceedsFromNotesPayable	20300000	USD
CY2018	us-gaap	Proceeds From Notes Payable ProceedsFromNotesPayable	29411000	USD
CY2020	us-gaap	Payments Of Debt Issuance Costs PaymentsOfDebtIssuanceCosts	0	USD
CY2019	us-gaap	Payments Of Debt Issuance Costs PaymentsOfDebtIssuanceCosts	231000	USD
CY2018	us-gaap	Payments Of Debt Issuance Costs PaymentsOfDebtIssuanceCosts	257000	USD
CY2020	us-gaap	Repayments Of Notes Payable RepaymentsOfNotesPayable	20300000	USD
CY2019	us-gaap	Repayments Of Notes Payable RepaymentsOfNotesPayable	49167000	USD
CY2018	us-gaap	Repayments Of Notes Payable RepaymentsOfNotesPayable	833000	USD
CY2020	us-gaap	Finance Lease Principal Payments FinanceLeasePrincipalPayments	5773000	USD
CY2019	us-gaap	Finance Lease Principal Payments FinanceLeasePrincipalPayments	1370000	USD
CY2018	us-gaap	Finance Lease Principal Payments FinanceLeasePrincipalPayments	1215000	USD
CY2020	us-gaap	Proceeds From Issuance Of Convertible Preferred Stock ProceedsFromIssuanceOfConvertiblePreferredStock	0	USD
CY2019	us-gaap	Proceeds From Issuance Of Convertible Preferred Stock ProceedsFromIssuanceOfConvertiblePreferredStock	0	USD
CY2018	us-gaap	Proceeds From Issuance Of Convertible Preferred Stock ProceedsFromIssuanceOfConvertiblePreferredStock	40000000	USD
CY2020	us-gaap	Proceeds From Stock Plans ProceedsFromStockPlans	9318000	USD
CY2019	us-gaap	Proceeds From Stock Plans ProceedsFromStockPlans	5402000	USD
CY2018	us-gaap	Proceeds From Stock Plans ProceedsFromStockPlans	0	USD
CY2020	us-gaap	Proceeds From Stock Options Exercised ProceedsFromStockOptionsExercised	15273000	USD
CY2019	us-gaap	Proceeds From Stock Options Exercised ProceedsFromStockOptionsExercised	5579000	USD
CY2018	us-gaap	Proceeds From Stock Options Exercised ProceedsFromStockOptionsExercised	1561000	USD
CY2020	fsly	Proceeds From Stock Options Exercised Early ProceedsFromStockOptionsExercisedEarly	0	USD
CY2018	fsly	Vesting Of Early Exercised Stock Options VestingOfEarlyExercisedStockOptions	337000	USD
CY2019Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	86229000	USD
CY2019	fsly	Proceeds From Stock Options Exercised Early ProceedsFromStockOptionsExercisedEarly	520000	USD
CY2018	fsly	Proceeds From Stock Options Exercised Early ProceedsFromStockOptionsExercisedEarly	1054000	USD
CY2020	fsly	Proceeds From Repayment Of Stockholders Note ProceedsFromRepaymentOfStockholdersNote	0	USD
CY2019	fsly	Proceeds From Repayment Of Stockholders Note ProceedsFromRepaymentOfStockholdersNote	74000	USD
CY2018	fsly	Proceeds From Repayment Of Stockholders Note ProceedsFromRepaymentOfStockholdersNote	50000	USD
CY2020	fsly	Payments For Repurchase Of Stock Options Exercised Early PaymentsForRepurchaseOfStockOptionsExercisedEarly	0	USD
CY2019	fsly	Payments For Repurchase Of Stock Options Exercised Early PaymentsForRepurchaseOfStockOptionsExercisedEarly	0	USD
CY2018	fsly	Payments For Repurchase Of Stock Options Exercised Early PaymentsForRepurchaseOfStockOptionsExercisedEarly	13000	USD
CY2020	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	272739000	USD
CY2019	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	168148000	USD
CY2018	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	69637000	USD
CY2020	us-gaap	Effect Of Exchange Rate On Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	-149000	USD
CY2019	us-gaap	Effect Of Exchange Rate On Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	99000	USD
CY2018	us-gaap	Effect Of Exchange Rate On Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	22000	USD
CY2020	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect	-22349000	USD
CY2019	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect	49266000	USD
CY2018	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect	5567000	USD
CY2018Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	36963000	USD
CY2017Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	31396000	USD
CY2020Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	63880000	USD
CY2019Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	86229000	USD
CY2018Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	36963000	USD
CY2020	us-gaap	Interest Paid Net InterestPaidNet	1590000	USD
CY2019	us-gaap	Interest Paid Net InterestPaidNet	5422000	USD
CY2018	us-gaap	Interest Paid Net InterestPaidNet	1833000	USD
CY2020	us-gaap	Income Taxes Paid Net IncomeTaxesPaidNet	1219000	USD
CY2019	us-gaap	Income Taxes Paid Net IncomeTaxesPaidNet	361000	USD
CY2018	us-gaap	Income Taxes Paid Net IncomeTaxesPaidNet	55000	USD
CY2020	us-gaap	Capital Expenditures Incurred But Not Yet Paid CapitalExpendituresIncurredButNotYetPaid	3184000	USD
CY2019	us-gaap	Capital Expenditures Incurred But Not Yet Paid CapitalExpendituresIncurredButNotYetPaid	7071000	USD
CY2018	us-gaap	Capital Expenditures Incurred But Not Yet Paid CapitalExpendituresIncurredButNotYetPaid	133000	USD
CY2020	fsly	Vesting Of Early Exercised Stock Options VestingOfEarlyExercisedStockOptions	467000	USD
CY2019	fsly	Vesting Of Early Exercised Stock Options VestingOfEarlyExercisedStockOptions	620000	USD
CY2020	us-gaap	Capital Lease Obligations Incurred CapitalLeaseObligationsIncurred	0	USD
CY2019	us-gaap	Capital Lease Obligations Incurred CapitalLeaseObligationsIncurred	7380000	USD
CY2018	us-gaap	Capital Lease Obligations Incurred CapitalLeaseObligationsIncurred	429000	USD
CY2020	fsly	Warrants Issued WarrantsIssued	0	USD
CY2019	fsly	Warrants Issued WarrantsIssued	0	USD
CY2018	fsly	Warrants Issued WarrantsIssued	1639000	USD
CY2020	fsly	Change In Other Assets From Change In Accounting Principle ChangeInOtherAssetsFromChangeInAccountingPrinciple	0	USD
CY2019	fsly	Change In Other Assets From Change In Accounting Principle ChangeInOtherAssetsFromChangeInAccountingPrinciple	5727000	USD
CY2018	fsly	Change In Other Assets From Change In Accounting Principle ChangeInOtherAssetsFromChangeInAccountingPrinciple	0	USD
CY2020	us-gaap	Conversion Of Stock Amount Converted1 ConversionOfStockAmountConverted1	0	USD
CY2019	us-gaap	Conversion Of Stock Amount Converted1 ConversionOfStockAmountConverted1	5665000	USD
CY2018	us-gaap	Conversion Of Stock Amount Converted1 ConversionOfStockAmountConverted1	0	USD
CY2020	fsly	Cashless Exercise Of Common Stock Warrants CashlessExerciseOfCommonStockWarrants	1557000	USD
CY2019	fsly	Cashless Exercise Of Common Stock Warrants CashlessExerciseOfCommonStockWarrants	1036000	USD
CY2018	fsly	Cashless Exercise Of Common Stock Warrants CashlessExerciseOfCommonStockWarrants	0	USD
CY2020	fsly	Initial Public Offering Costs Incurred But Not Yet Paid InitialPublicOfferingCostsIncurredButNotYetPaid	0	USD
CY2019	fsly	Initial Public Offering Costs Incurred But Not Yet Paid InitialPublicOfferingCostsIncurredButNotYetPaid	130000	USD
CY2018	fsly	Initial Public Offering Costs Incurred But Not Yet Paid InitialPublicOfferingCostsIncurredButNotYetPaid	0	USD
CY2020	us-gaap	Employee Service Share Based Compensation Allocation Of Recognized Period Costs Capitalized Amount EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount	2034000	USD
CY2019	us-gaap	Employee Service Share Based Compensation Allocation Of Recognized Period Costs Capitalized Amount EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount	441000	USD
CY2018	us-gaap	Employee Service Share Based Compensation Allocation Of Recognized Period Costs Capitalized Amount EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount	0	USD
CY2020	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	23827000	USD
CY2019	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	0	USD
CY2018	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	0	USD
CY2020	us-gaap	Right Of Use Asset Obtained In Exchange For Finance Lease Liability RightOfUseAssetObtainedInExchangeForFinanceLeaseLiability	22541000	USD
CY2019	us-gaap	Right Of Use Asset Obtained In Exchange For Finance Lease Liability RightOfUseAssetObtainedInExchangeForFinanceLeaseLiability	0	USD
CY2018	us-gaap	Right Of Use Asset Obtained In Exchange For Finance Lease Liability RightOfUseAssetObtainedInExchangeForFinanceLeaseLiability	0	USD
CY2020	us-gaap	Stock Issued1 StockIssued1	536432000	USD
CY2019	us-gaap	Stock Issued1 StockIssued1	0	USD
CY2018	us-gaap	Stock Issued1 StockIssued1	0	USD
CY2020Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	62900000	USD
CY2019Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	16142000	USD
CY2018Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	36963000	USD
CY2020Q4	us-gaap	Restricted Cash Current RestrictedCashCurrent	87000	USD
CY2019Q4	us-gaap	Restricted Cash Current RestrictedCashCurrent	70087000	USD
CY2018Q4	us-gaap	Restricted Cash Current RestrictedCashCurrent	0	USD
CY2020Q4	us-gaap	Restricted Cash Equivalents RestrictedCashEquivalents	893000	USD
CY2019Q4	us-gaap	Restricted Cash Equivalents RestrictedCashEquivalents	0	USD
CY2018Q4	us-gaap	Restricted Cash Equivalents RestrictedCashEquivalents	0	USD
CY2020Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	63880000	USD
CY2019Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	86229000	USD
CY2018Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	36963000	USD
CY2020	us-gaap	Nature Of Operations NatureOfOperations	Nature of Business<div style="margin-bottom:12pt;text-indent:27pt"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%">Fastly, Inc. has built an edge cloud platform that can process, serve, and secure its customer’s applications as close to their end users as possible. Our edge network spans across 56 markets, as of December 31, 2020. We were incorporated in Delaware in 2011 and are headquartered in San Francisco, California.</span></div><div style="margin-bottom:12pt;text-indent:27pt"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%">As used herein, "Fastly," "we," "our," "the Company," and similar terms include Fastly, Inc. and its subsidiaries, unless the context indicates otherwise.</span></div><div style="margin-bottom:12pt"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-style:italic;font-weight:700;line-height:120%">Stock Split</span></div><div style="margin-bottom:12pt;text-indent:27pt"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%">On May 3, 2019, we implemented a 1-for-2 reverse stock split of our stock. All shares of common stock, stock-based instruments, and per-share data included in these financial statements give effect to the stock split and the changes in authorized shares have been adjusted retroactively for all periods presented.</span></div><div style="margin-bottom:12pt"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-style:italic;font-weight:700;line-height:120%">Initial Public Offering ("IPO")</span></div><div style="margin-bottom:12pt;text-indent:27pt"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%">On May 21, 2019 we completed an IPO in which we sold 12,937,500 shares of our newly authorized Class A common stock, which included 1,687,500 shares sold pursuant to the exercise by the underwriters of an option to purchase additional shares, at the public offering price of $16.00 per share. We received net proceeds of $192.5 million, after deducting underwriting discounts and commissions, from sales of our shares in the IPO. The net proceeds include additional proceeds of $25.1 million, net of underwriters' discounts and commissions, from the exercise of the underwriters' option to purchase an additional 1,687,500 shares of our Class A common stock. Prior to the closing of the IPO, all shares of common stock then outstanding were reclassified as Class B common stock. </span></div><div style="margin-bottom:12pt;text-indent:27pt"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%">Immediately upon the closing of the IPO, all shares of convertible preferred stock then outstanding were converted into 53,630,213 shares of Class B common stock on a one-to-one basis. Prior to the IPO, we had seven outstanding series of convertible preferred stock each with a par value of $0.00002 per share, convertible at the option of the holder, that was classified as temporary equity on our consolidated balance sheet. On May 17, 2019, immediately upon closing of the IPO, our convertible preferred stock was automatically converted to shares of our Class B common stock. As of both December 31, 2019 and 2020, we had zero convertible preferred stock issued or outstanding.</span></div><div style="margin-bottom:12pt"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-style:italic;font-weight:700;line-height:120%">Follow-on Public Offering</span></div><div style="margin-bottom:12pt;text-indent:27pt"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%">On May 26, 2020, we completed a follow-on public offering in which we sold 6,900,000 shares of Class A common stock, which included 900,000 shares sold pursuant to the exercise by the underwriters of an option to purchase additional shares, at the public offering price of $41.50 per share. We received net proceeds of $274.9 million, after deducting underwriting discounts and commissions, from sales of our shares in the public offering.</span></div>
CY2020Q4	fsly	Operating Markets OperatingMarkets	56	operatingMarket
CY2019Q2	fsly	Convertible Preferred Stock Number Of Series ConvertiblePreferredStockNumberOfSeries	7	stockSeries
CY2019Q2	us-gaap	Temporary Equity Par Or Stated Value Per Share TemporaryEquityParOrStatedValuePerShare	0.00002
CY2020Q4	us-gaap	Temporary Equity Shares Issued TemporaryEquitySharesIssued	0	shares
CY2019Q4	us-gaap	Temporary Equity Shares Outstanding TemporaryEquitySharesOutstanding	0	shares
CY2019Q4	us-gaap	Temporary Equity Shares Issued TemporaryEquitySharesIssued	0	shares
CY2020Q4	us-gaap	Temporary Equity Shares Outstanding TemporaryEquitySharesOutstanding	0	shares
CY2020	us-gaap	Basis Of Accounting BasisOfAccounting	<div style="margin-bottom:12pt"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-style:italic;font-weight:700;line-height:120%">Basis of Presentation</span></div><div style="margin-bottom:12pt;text-indent:27pt"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%">The consolidated financial statements have been prepared in accordance with United States generally accepted accounting principles ("U.S. GAAP"). </span></div><div style="margin-bottom:12pt;text-indent:27pt"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%">Certain changes in presentation have been made to conform the prior period presentation to the current period reporting. Such reclassifications did not affect total revenues, operating income, or net income. We have made certain presentation changes to distinguish and disclose as a separate line item, the non-cash amortization expense of our deferred contract costs balance from other assets within operating cash flows in the Consolidated Statements of Cash Flows. With the adoption of the new leasing standard Accounting Standards Codification No. 842, Leases ("ASC 842"), we have also made certain presentation changes to distinguish and disclose as separate line items, our current and noncurrent finance leases liabilities from our current and noncurrent debt amounts in the Consolidated Balance Sheets.</span></div>
CY2020	us-gaap	Use Of Estimates UseOfEstimates	<div style="margin-bottom:12pt"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-style:italic;font-weight:700;line-height:120%">Use of Estimates</span></div><div style="margin-bottom:12pt;text-indent:27pt"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%">The preparation of our consolidated financial statements requires us to make estimates, judgments, and assumptions that affect the reported amounts of assets, liabilities, revenue, costs and expenses, and related disclosures. Actual results and outcomes could differ significantly from our estimates, judgments, and assumptions. Significant estimates, judgments, and assumptions used in these financial statements include, but are not limited to, those related to revenue, accounts receivable and related reserves, fair value of assets acquired and liabilities assumed for business combinations, useful lives and realizability of long-lived assets, income tax reserves, and accounting for stock-based compensation. Estimates are periodically reviewed in light of changes in circumstances, facts, and experience. The effects of material revisions in estimates are reflected in the consolidated financial statements in the period of change and prospectively from the date of the change in estimate.</span></div><div style="margin-bottom:12pt;text-indent:27pt"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%">The ongoing global COVID-19 pandemic has impacted many operational aspects of our business and may continue to do so in the future. We assessed the impact that COVID-19 had on our results of operations, including, but not limited to an assessment of our allowance for doubtful accounts, the carrying value of short-term and long-term investments, the carrying value of goodwill and other long-lived assets, and the impact to revenue recognition and cost of revenues. While the COVID-19 pandemic has not had a material adverse impact on our financial operations to date, the future impacts of the pandemic and any resulting economic impact are largely unknown and rapidly evolving. We will continue to actively monitor the impact that COVID-19 has on the results of our business operations, and may make decisions required by federal, state or local authorities, or that are determined to be in the best interests of our employees, customers, partners, suppliers and stockholders. As a result, our estimates and judgments may change materially as new events occur or additional information becomes available to us.</span></div>
CY2019Q4	us-gaap	Restricted Cash RestrictedCash	70100000	USD
CY2020Q4	fsly	Cash Released From Restriction CashReleasedFromRestriction	70000000.0	USD
CY2018	us-gaap	Advertising Expense AdvertisingExpense	500000	USD
CY2020Q4	us-gaap	Restricted Cash RestrictedCash	1000000.0	USD
CY2020Q4	us-gaap	Restricted Cash Equivalents RestrictedCashEquivalents	900000	USD
CY2020	us-gaap	Concentration Risk Credit Risk ConcentrationRiskCreditRisk	<div style="margin-bottom:12pt"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-style:italic;font-weight:700;line-height:120%">Concentrations of Credit Risk</span></div><div style="margin-bottom:12pt;text-indent:27pt"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%">Financial instruments that potentially subject us to significant concentration of credit risk consist primarily of cash, cash equivalents, marketable securities, and accounts receivable. The primary focus of our investment strategy is to preserve capital and meet liquidity requirements. Our investment policy addresses the level of credit exposure by limiting the concentration in any one corporate issuer or sector and establishing a minimum allowable credit rating. To manage the risk exposure, we invest cash equivalents and marketable securities in a variety of fixed income securities, including government and investment-grade debt securities and money market funds. We place our cash primarily in checking and money market accounts with reputable financial institutions. Deposits held with these financial institutions may exceed the amount of insurance provided on such deposits, if any.</span></div>Concentrations of credit risk with respect to accounts receivable are primarily limited to certain customers to which we make substantial sales. Our customer base consists of a large number of geographically dispersed customers diversified across several industries. To reduce risk, we routinely assess the financial strength of our customers. Based on such assessments, we believe that our accounts receivable credit risk exposure is limited.
CY2020	us-gaap	Advertising Expense AdvertisingExpense	3800000	USD
CY2019	us-gaap	Advertising Expense AdvertisingExpense	1400000	USD
CY2020Q1	us-gaap	Operating Lease Right Of Use Asset OperatingLeaseRightOfUseAsset	54700000	USD
CY2020Q1	us-gaap	Operating Lease Liability OperatingLeaseLiability	56300000	USD
CY2020	us-gaap	Revenue From Contract With Customer Including Assessed Tax RevenueFromContractWithCustomerIncludingAssessedTax	290874000	USD
CY2019	us-gaap	Revenue From Contract With Customer Including Assessed Tax RevenueFromContractWithCustomerIncludingAssessedTax	200462000	USD
CY2018	us-gaap	Revenue From Contract With Customer Including Assessed Tax RevenueFromContractWithCustomerIncludingAssessedTax	144563000	USD
CY2020Q4	fsly	Enterprise Customer Threshold EnterpriseCustomerThreshold	100000	USD
CY2020	us-gaap	Revenue From Contract With Customer Including Assessed Tax RevenueFromContractWithCustomerIncludingAssessedTax	290874000	USD
CY2019	us-gaap	Revenue From Contract With Customer Including Assessed Tax RevenueFromContractWithCustomerIncludingAssessedTax	200462000	USD
CY2018	us-gaap	Revenue From Contract With Customer Including Assessed Tax RevenueFromContractWithCustomerIncludingAssessedTax	144563000	USD
CY2020	us-gaap	Revenue Performance Obligation Description Of Payment Terms RevenuePerformanceObligationDescriptionOfPaymentTerms	Payment terms on invoiced amounts are typically 15 to 45 days.
CY2020Q4	us-gaap	Contract With Customer Asset Net ContractWithCustomerAssetNet	387000	USD
CY2019Q4	us-gaap	Contract With Customer Asset Net ContractWithCustomerAssetNet	271000	USD
CY2020Q4	us-gaap	Contract With Customer Liability ContractWithCustomerLiability	18020000	USD
CY2019Q4	us-gaap	Contract With Customer Liability ContractWithCustomerLiability	317000	USD
CY2020Q4	us-gaap	Contract With Customer Liability Increase Decrease For Contract Acquired In Business Combination ContractWithCustomerLiabilityIncreaseDecreaseForContractAcquiredInBusinessCombination	14600000	USD
CY2020	us-gaap	Contract With Customer Liability Revenue Recognized ContractWithCustomerLiabilityRevenueRecognized	310000	USD
CY2019	us-gaap	Contract With Customer Liability Revenue Recognized ContractWithCustomerLiabilityRevenueRecognized	1539000	USD
CY2020Q4	us-gaap	Revenue Remaining Performance Obligation RevenueRemainingPerformanceObligation	155300000	USD
CY2020Q4	us-gaap	Revenue Remaining Performance Obligation Percentage RevenueRemainingPerformanceObligationPercentage	0.71
CY2020Q4	us-gaap	Revenue Remaining Performance Obligation Expected Timing Of Satisfaction Period1 RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1	P12M
CY2020Q4	us-gaap	Capitalized Contract Cost Net Noncurrent CapitalizedContractCostNetNoncurrent	19332000	USD
CY2019Q4	us-gaap	Capitalized Contract Cost Net Noncurrent CapitalizedContractCostNetNoncurrent	6804000	USD
CY2020	us-gaap	Capitalized Contract Cost Amortization CapitalizedContractCostAmortization	3500000	USD
CY2019	us-gaap	Capitalized Contract Cost Amortization CapitalizedContractCostAmortization	2300000	USD
CY2020Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	62900000	USD
CY2019Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	16142000	USD
CY2020Q4	us-gaap	Available For Sale Securities Debt Securities Current AvailableForSaleSecuritiesDebtSecuritiesCurrent	131283000	USD
CY2019Q4	us-gaap	Available For Sale Securities Debt Securities Current AvailableForSaleSecuritiesDebtSecuritiesCurrent	114967000	USD
CY2020Q4	us-gaap	Available For Sale Securities Debt Securities Noncurrent AvailableForSaleSecuritiesDebtSecuritiesNoncurrent	20448000	USD
CY2019Q4	us-gaap	Available For Sale Securities Debt Securities Noncurrent AvailableForSaleSecuritiesDebtSecuritiesNoncurrent	0	USD
CY2020Q4	us-gaap	Available For Sale Securities Debt Securities AvailableForSaleSecuritiesDebtSecurities	151731000	USD
CY2019Q4	us-gaap	Available For Sale Securities Debt Securities AvailableForSaleSecuritiesDebtSecurities	114967000	USD
CY2019Q4	us-gaap	Cash Equivalents At Carrying Value CashEquivalentsAtCarryingValue	4519000	USD
CY2020Q4	us-gaap	Available For Sale Debt Securities Amortized Cost Basis AvailableForSaleDebtSecuritiesAmortizedCostBasis	151626000	USD
CY2020Q4	us-gaap	Available For Sale Debt Securities Accumulated Gross Unrealized Gain Before Tax AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax	110000	USD
CY2020Q4	us-gaap	Available For Sale Debt Securities Accumulated Gross Unrealized Loss Before Tax AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax	5000	USD
CY2020Q4	us-gaap	Available For Sale Securities Debt Securities AvailableForSaleSecuritiesDebtSecurities	151731000	USD
CY2019Q4	us-gaap	Available For Sale Debt Securities Amortized Cost Basis AvailableForSaleDebtSecuritiesAmortizedCostBasis	114870000	USD
CY2019Q4	us-gaap	Available For Sale Debt Securities Accumulated Gross Unrealized Gain Before Tax AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax	98000	USD
CY2019Q4	us-gaap	Available For Sale Debt Securities Accumulated Gross Unrealized Loss Before Tax AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax	1000	USD
CY2019Q4	us-gaap	Available For Sale Securities Debt Securities AvailableForSaleSecuritiesDebtSecurities	114967000	USD
CY2019Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position12 Months Or Longer Number Of Positions DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerNumberOfPositions	0	security
CY2020Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position12 Months Or Longer Number Of Positions DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerNumberOfPositions	0	security
CY2020Q4	us-gaap	Cash Equivalents At Carrying Value CashEquivalentsAtCarryingValue	41627000	USD
CY2020Q4	us-gaap	Available For Sale Securities Debt Securities AvailableForSaleSecuritiesDebtSecurities	151731000	USD
CY2020Q4	us-gaap	Restricted Cash And Cash Equivalents RestrictedCashAndCashEquivalents	980000	USD
CY2020Q4	us-gaap	Assets Fair Value Disclosure AssetsFairValueDisclosure	194338000	USD
CY2020Q4	us-gaap	Restricted Cash RestrictedCash	1000000.0	USD
CY2020Q4	us-gaap	Restricted Cash Noncurrent RestrictedCashNoncurrent	900000	USD
CY2019Q4	us-gaap	Available For Sale Securities Debt Securities AvailableForSaleSecuritiesDebtSecurities	114967000	USD
CY2019Q4	us-gaap	Restricted Cash And Cash Equivalents RestrictedCashAndCashEquivalents	70087000	USD
CY2019Q4	us-gaap	Assets Fair Value Disclosure AssetsFairValueDisclosure	189573000	USD
CY2020	us-gaap	Business Acquisitions Pro Forma Revenue BusinessAcquisitionsProFormaRevenue	313665000	USD
CY2019	us-gaap	Business Acquisitions Pro Forma Revenue BusinessAcquisitionsProFormaRevenue	218529000	USD
CY2020	us-gaap	Business Acquisitions Pro Forma Net Income Loss BusinessAcquisitionsProFormaNetIncomeLoss	159248000	USD
CY2019	us-gaap	Business Acquisitions Pro Forma Net Income Loss BusinessAcquisitionsProFormaNetIncomeLoss	178124000	USD
CY2019Q4	us-gaap	Allowance For Doubtful Accounts Receivable Current AllowanceForDoubtfulAccountsReceivableCurrent	1816000	USD
CY2018Q4	us-gaap	Allowance For Doubtful Accounts Receivable Current AllowanceForDoubtfulAccountsReceivableCurrent	1679000	USD
CY2020	us-gaap	Provision For Doubtful Accounts ProvisionForDoubtfulAccounts	1719000	USD
CY2019	us-gaap	Provision For Doubtful Accounts ProvisionForDoubtfulAccounts	360000	USD
CY2020	us-gaap	Allowance For Doubtful Accounts Receivable Write Offs AllowanceForDoubtfulAccountsReceivableWriteOffs	287000	USD
CY2019	us-gaap	Allowance For Doubtful Accounts Receivable Write Offs AllowanceForDoubtfulAccountsReceivableWriteOffs	223000	USD
CY2020Q4	us-gaap	Allowance For Doubtful Accounts Receivable Current AllowanceForDoubtfulAccountsReceivableCurrent	3248000	USD
CY2019Q4	us-gaap	Allowance For Doubtful Accounts Receivable Current AllowanceForDoubtfulAccountsReceivableCurrent	1816000	USD
CY2020Q4	us-gaap	Property Plant And Equipment And Finance Lease Right Of Use Asset Before Accumulated Depreciation And Amortization PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetBeforeAccumulatedDepreciationAndAmortization	157632000	USD
CY2019Q4	us-gaap	Property Plant And Equipment And Finance Lease Right Of Use Asset Before Accumulated Depreciation And Amortization PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetBeforeAccumulatedDepreciationAndAmortization	108276000	USD
CY2020Q4	us-gaap	Property Plant And Equipment And Finance Lease Right Of Use Asset Accumulated Depreciation And Amortization PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization	61653000	USD
CY2019Q4	us-gaap	Property Plant And Equipment And Finance Lease Right Of Use Asset Accumulated Depreciation And Amortization PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization	48239000	USD
CY2020Q4	us-gaap	Property Plant And Equipment And Finance Lease Right Of Use Asset After Accumulated Depreciation And Amortization PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization	95979000	USD
CY2019Q4	us-gaap	Property Plant And Equipment And Finance Lease Right Of Use Asset After Accumulated Depreciation And Amortization PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization	60037000	USD
CY2020	us-gaap	Depreciation And Amortization DepreciationAndAmortization	19800000	USD
CY2019	us-gaap	Depreciation And Amortization DepreciationAndAmortization	16400000	USD
CY2020Q4	us-gaap	Finance Lease Right Of Use Asset Before Accumulated Amortization FinanceLeaseRightOfUseAssetBeforeAccumulatedAmortization	36200000	USD
CY2019Q4	us-gaap	Finance Lease Right Of Use Asset Before Accumulated Amortization FinanceLeaseRightOfUseAssetBeforeAccumulatedAmortization	13700000	USD
CY2020Q4	us-gaap	Finance Lease Right Of Use Asset Accumulated Amortization FinanceLeaseRightOfUseAssetAccumulatedAmortization	6700000	USD
CY2019Q4	us-gaap	Finance Lease Right Of Use Asset Accumulated Amortization FinanceLeaseRightOfUseAssetAccumulatedAmortization	3800000	USD
CY2020Q4	us-gaap	Employee Related Liabilities Current EmployeeRelatedLiabilitiesCurrent	17840000	USD
CY2019Q4	us-gaap	Employee Related Liabilities Current EmployeeRelatedLiabilitiesCurrent	8734000	USD
CY2020Q4	us-gaap	Sales And Excise Tax Payable Current SalesAndExciseTaxPayableCurrent	6274000	USD
CY2019Q4	us-gaap	Sales And Excise Tax Payable Current SalesAndExciseTaxPayableCurrent	3938000	USD
CY2020Q4	fsly	Accrued Colocation And Bandwidth Costs AccruedColocationAndBandwidthCosts	3644000	USD
CY2019Q4	fsly	Accrued Colocation And Bandwidth Costs AccruedColocationAndBandwidthCosts	3237000	USD
CY2020Q4	fsly	Accrued Acquisition Related Costs Current AccruedAcquisitionRelatedCostsCurrent	2208000	USD
CY2020Q4	us-gaap	Lessee Operating Lease Liability Payments Due Next Twelve Months LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths	23095000	USD
CY2019Q4	fsly	Accrued Acquisition Related Costs Current AccruedAcquisitionRelatedCostsCurrent	0	USD
CY2020Q4	us-gaap	Other Accrued Liabilities Current OtherAccruedLiabilitiesCurrent	4368000	USD
CY2019Q4	us-gaap	Other Accrued Liabilities Current OtherAccruedLiabilitiesCurrent	3969000	USD
CY2020Q4	us-gaap	Accrued Liabilities Current AccruedLiabilitiesCurrent	34334000	USD
CY2019Q4	us-gaap	Accrued Liabilities Current AccruedLiabilitiesCurrent	19878000	USD
CY2020Q4	us-gaap	Contract With Customer Liability Current ContractWithCustomerLiabilityCurrent	15916000	USD
CY2019Q4	us-gaap	Contract With Customer Liability Current ContractWithCustomerLiabilityCurrent	317000	USD
CY2020Q4	fsly	Accrued Computer And Networking Equipment AccruedComputerAndNetworkingEquipment	3126000	USD
CY2019Q4	fsly	Accrued Computer And Networking Equipment AccruedComputerAndNetworkingEquipment	7060000	USD
CY2020Q4	fsly	Liability For Early Exercised Stock Options Current LiabilityForEarlyExercisedStockOptionsCurrent	255000	USD
CY2019Q4	fsly	Liability For Early Exercised Stock Options Current LiabilityForEarlyExercisedStockOptionsCurrent	467000	USD
CY2020Q4	us-gaap	Other Sundry Liabilities Current OtherSundryLiabilitiesCurrent	380000	USD
CY2019Q4	us-gaap	Other Sundry Liabilities Current OtherSundryLiabilitiesCurrent	325000	USD
CY2020Q4	us-gaap	Other Liabilities Current OtherLiabilitiesCurrent	19677000	USD
CY2019Q4	us-gaap	Other Liabilities Current OtherLiabilitiesCurrent	8169000	USD
CY2020Q4	us-gaap	Contract With Customer Liability Noncurrent ContractWithCustomerLiabilityNoncurrent	2104000	USD
CY2019Q4	us-gaap	Contract With Customer Liability Noncurrent ContractWithCustomerLiabilityNoncurrent	0	USD
CY2020Q4	fsly	Accrued Payroll Taxes Noncurrent Cares Act AccruedPayrollTaxesNoncurrentCARESAct	1676000	USD
CY2019Q4	fsly	Accrued Payroll Taxes Noncurrent Cares Act AccruedPayrollTaxesNoncurrentCARESAct	0	USD
CY2020Q4	us-gaap	Deferred Rent Credit Noncurrent DeferredRentCreditNoncurrent	0	USD
CY2019Q4	us-gaap	Deferred Rent Credit Noncurrent DeferredRentCreditNoncurrent	634000	USD
CY2020Q4	us-gaap	Other Sundry Liabilities Noncurrent OtherSundryLiabilitiesNoncurrent	620000	USD
CY2019Q4	us-gaap	Other Sundry Liabilities Noncurrent OtherSundryLiabilitiesNoncurrent	404000	USD
CY2020Q4	us-gaap	Other Liabilities Noncurrent OtherLiabilitiesNoncurrent	4400000	USD
CY2019Q4	us-gaap	Other Liabilities Noncurrent OtherLiabilitiesNoncurrent	1038000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent	-12000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent	232000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent	-190000	USD
CY2020	fsly	Subleases Remaining Lease Terms SubleasesRemainingLeaseTerms	P1Y
CY2020	us-gaap	Sublease Income SubleaseIncome	1300000	USD
CY2019	us-gaap	Sublease Income SubleaseIncome	1200000	USD
CY2018	us-gaap	Sublease Income SubleaseIncome	900000	USD
CY2020	us-gaap	Operating Lease Cost OperatingLeaseCost	21765000	USD
CY2020	us-gaap	Variable Lease Cost VariableLeaseCost	4363000	USD
CY2020	us-gaap	Short Term Lease Cost ShortTermLeaseCost	0	USD
CY2020	fsly	Operating Variable And Short Term Lease Costs OperatingVariableAndShortTermLeaseCosts	26128000	USD
CY2020	us-gaap	Finance Lease Right Of Use Asset Amortization FinanceLeaseRightOfUseAssetAmortization	2858000	USD
CY2020	us-gaap	Finance Lease Interest Expense FinanceLeaseInterestExpense	688000	USD
CY2020	fsly	Finance Lease Cost FinanceLeaseCost	3546000	USD
CY2020Q4	us-gaap	Finance Lease Liability Payments Due Next Twelve Months FinanceLeaseLiabilityPaymentsDueNextTwelveMonths	12115000	USD
CY2020	us-gaap	Operating Lease Payments OperatingLeasePayments	18264000	USD
CY2020	us-gaap	Finance Lease Principal Payments FinanceLeasePrincipalPayments	5773000	USD
CY2020	us-gaap	Finance Lease Interest Payment On Liability FinanceLeaseInterestPaymentOnLiability	688000	USD
CY2020	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	23827000	USD
CY2020	us-gaap	Right Of Use Asset Obtained In Exchange For Finance Lease Liability RightOfUseAssetObtainedInExchangeForFinanceLeaseLiability	22541000	USD
CY2020Q4	us-gaap	Operating Lease Weighted Average Remaining Lease Term1 OperatingLeaseWeightedAverageRemainingLeaseTerm1	P4Y5M8D
CY2020Q4	us-gaap	Finance Lease Weighted Average Remaining Lease Term1 FinanceLeaseWeightedAverageRemainingLeaseTerm1	P2Y6M3D
CY2020Q4	us-gaap	Operating Lease Weighted Average Discount Rate Percent OperatingLeaseWeightedAverageDiscountRatePercent	0.0568
CY2020Q4	us-gaap	Finance Lease Weighted Average Discount Rate Percent FinanceLeaseWeightedAverageDiscountRatePercent	0.0512
CY2020Q4	fsly	Lessee Operating Lease Lease Not Yet Commenced Commitment Amount LesseeOperatingLeaseLeaseNotYetCommencedCommitmentAmount	7900000	USD
CY2020Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Two LesseeOperatingLeaseLiabilityPaymentsDueYearTwo	17010000	USD
CY2020Q4	us-gaap	Finance Lease Liability Payments Due Year Two FinanceLeaseLiabilityPaymentsDueYearTwo	9447000	USD
CY2020Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Three LesseeOperatingLeaseLiabilityPaymentsDueYearThree	10706000	USD
CY2020Q4	us-gaap	Finance Lease Liability Payments Due Year Three FinanceLeaseLiabilityPaymentsDueYearThree	5921000	USD
CY2020Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Four LesseeOperatingLeaseLiabilityPaymentsDueYearFour	7965000	USD
CY2020Q4	us-gaap	Finance Lease Liability Payments Due Year Four FinanceLeaseLiabilityPaymentsDueYearFour	0	USD
CY2020Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Five LesseeOperatingLeaseLiabilityPaymentsDueYearFive	7416000	USD
CY2020Q4	us-gaap	Finance Lease Liability Payments Due Year Five FinanceLeaseLiabilityPaymentsDueYearFive	0	USD
CY2020Q4	us-gaap	Lessee Operating Lease Liability Payments Due After Year Five LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive	9888000	USD
CY2020Q4	us-gaap	Finance Lease Liability Payments Due After Year Five FinanceLeaseLiabilityPaymentsDueAfterYearFive	0	USD
CY2020Q4	us-gaap	Lessee Operating Lease Liability Payments Due LesseeOperatingLeaseLiabilityPaymentsDue	76080000	USD
CY2020Q4	us-gaap	Finance Lease Liability Payments Due FinanceLeaseLiabilityPaymentsDue	27483000	USD
CY2020Q4	us-gaap	Lessee Operating Lease Liability Undiscounted Excess Amount LesseeOperatingLeaseLiabilityUndiscountedExcessAmount	9591000	USD
CY2020Q4	us-gaap	Finance Lease Liability Undiscounted Excess Amount FinanceLeaseLiabilityUndiscountedExcessAmount	1742000	USD
CY2020Q4	us-gaap	Operating Lease Liability OperatingLeaseLiability	66489000	USD
CY2020Q4	us-gaap	Finance Lease Liability FinanceLeaseLiability	25741000	USD
CY2019Q4	us-gaap	Goodwill Goodwill	372000	USD
CY2018Q4	us-gaap	Goodwill Goodwill	360000	USD
CY2020	us-gaap	Goodwill Acquired During Period GoodwillAcquiredDuringPeriod	635204000	USD
CY2019	us-gaap	Goodwill Acquired During Period GoodwillAcquiredDuringPeriod	0	USD
CY2020	us-gaap	Goodwill Foreign Currency Translation Gain Loss GoodwillForeignCurrencyTranslationGainLoss	14000	USD
CY2019	us-gaap	Goodwill Foreign Currency Translation Gain Loss GoodwillForeignCurrencyTranslationGainLoss	12000	USD
CY2020Q4	us-gaap	Goodwill Goodwill	635590000	USD
CY2019Q4	us-gaap	Goodwill Goodwill	372000	USD
CY2019	us-gaap	Goodwill Impairment Loss GoodwillImpairmentLoss	0	USD
CY2018	us-gaap	Goodwill Impairment Loss GoodwillImpairmentLoss	0	USD
CY2020	us-gaap	Goodwill Impairment Loss GoodwillImpairmentLoss	0	USD
CY2020Q4	us-gaap	Intangible Assets Gross Excluding Goodwill IntangibleAssetsGrossExcludingGoodwill	127398000	USD
CY2020Q4	us-gaap	Finite Lived Intangible Assets Accumulated Amortization FiniteLivedIntangibleAssetsAccumulatedAmortization	5656000	USD
CY2020Q4	us-gaap	Intangible Assets Net Excluding Goodwill IntangibleAssetsNetExcludingGoodwill	121742000	USD
CY2020Q4	us-gaap	Extinguishment Of Debt Amount ExtinguishmentOfDebtAmount	20300000	USD
CY2020Q4	us-gaap	Purchase Obligation PurchaseObligation	59588000	USD
CY2019Q4	us-gaap	Intangible Assets Gross Excluding Goodwill IntangibleAssetsGrossExcludingGoodwill	1487000	USD
CY2019Q4	us-gaap	Finite Lived Intangible Assets Accumulated Amortization FiniteLivedIntangibleAssetsAccumulatedAmortization	362000	USD
CY2019Q4	us-gaap	Intangible Assets Net Excluding Goodwill IntangibleAssetsNetExcludingGoodwill	1125000	USD
CY2020	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	5300000	USD
CY2019	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	100000	USD
CY2018	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	100000	USD
CY2020Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Next Twelve Months FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths	21143000	USD
CY2020Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Two FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo	20765000	USD
CY2020Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Three FiniteLivedIntangibleAssetsAmortizationExpenseYearThree	19665000	USD
CY2020Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Four FiniteLivedIntangibleAssetsAmortizationExpenseYearFour	18830000	USD
CY2020Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Five FiniteLivedIntangibleAssetsAmortizationExpenseYearFive	16352000	USD
CY2020Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense After Year Five FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive	24619000	USD
CY2020Q4	us-gaap	Finite Lived Intangible Assets Net FiniteLivedIntangibleAssetsNet	121374000	USD
CY2020Q4	fsly	Cash Released From Restriction CashReleasedFromRestriction	70000000.0	USD
CY2020	us-gaap	Interest Expense Debt InterestExpenseDebt	900000	USD
CY2019	us-gaap	Interest Expense Debt InterestExpenseDebt	5200000	USD
CY2018	us-gaap	Interest Expense Debt InterestExpenseDebt	1900000	USD
CY2020Q4	us-gaap	Purchase Obligation Due In Next Twelve Months PurchaseObligationDueInNextTwelveMonths	35685000	USD
CY2020Q4	us-gaap	Purchase Obligation Due In Second Year PurchaseObligationDueInSecondYear	14903000	USD
CY2020Q4	us-gaap	Purchase Obligation Due In Third Year PurchaseObligationDueInThirdYear	9000000	USD
CY2020Q4	us-gaap	Purchase Obligation Due In Fourth Year PurchaseObligationDueInFourthYear	0	USD
CY2020Q4	us-gaap	Purchase Obligation Due In Fifth Year PurchaseObligationDueInFifthYear	0	USD
CY2020Q4	us-gaap	Purchase Obligation Due After Fifth Year PurchaseObligationDueAfterFifthYear	0	USD
CY2020Q4	us-gaap	Sales And Excise Tax Payable Current And Noncurrent SalesAndExciseTaxPayableCurrentAndNoncurrent	6300000	USD
CY2019Q4	us-gaap	Sales And Excise Tax Payable Current And Noncurrent SalesAndExciseTaxPayableCurrentAndNoncurrent	3900000	USD
CY2020Q3	fsly	Loss Contingency Pending Claims Number Consolidated LossContingencyPendingClaimsNumberConsolidated	2	lawsuit
CY2020Q3	us-gaap	Loss Contingency Pending Claims Number LossContingencyPendingClaimsNumber	1	lawsuit
CY2019Q2	us-gaap	Preferred Stock Shares Authorized PreferredStockSharesAuthorized	10000000.0	shares
CY2019Q2	us-gaap	Preferred Stock Par Or Stated Value Per Share PreferredStockParOrStatedValuePerShare	0.00002
CY2020Q4	us-gaap	Preferred Stock Shares Outstanding PreferredStockSharesOutstanding	0	shares
CY2019Q4	us-gaap	Preferred Stock Shares Outstanding PreferredStockSharesOutstanding	0	shares
CY2020Q4	us-gaap	Preferred Stock Shares Issued PreferredStockSharesIssued	0	shares
CY2019Q4	us-gaap	Preferred Stock Shares Issued PreferredStockSharesIssued	0	shares
CY2017Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Number ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber	10370000	shares
CY2017Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice	1.92
CY2017	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Outstanding Weighted Average Remaining Contractual Term2 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2	P8Y
CY2017Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue	16901000	USD
CY2018	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Gross ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross	3984000	shares
CY2018	us-gaap	Share Based Compensation Arrangements By Share Based Payment Award Options Grants In Period Weighted Average Exercise Price ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice	5.32
CY2018	us-gaap	Stock Issued During Period Shares Stock Options Exercised StockIssuedDuringPeriodSharesStockOptionsExercised	1264000	shares
CY2018	us-gaap	Share Based Compensation Arrangements By Share Based Payment Award Options Exercises In Period Weighted Average Exercise Price ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice	2.1
CY2018	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Forfeitures And Expirations In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod	880000	shares
CY2018	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Forfeitures And Expirations In Period Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriodWeightedAverageExercisePrice	2.64
CY2018Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Number ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber	12210000	shares
CY2018Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice	2.96
CY2018	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Outstanding Weighted Average Remaining Contractual Term2 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2	P7Y9M18D
CY2018Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue	64590000	USD
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Gross ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross	2516000	shares
CY2019	us-gaap	Share Based Compensation Arrangements By Share Based Payment Award Options Grants In Period Weighted Average Exercise Price ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice	10.87
CY2019	us-gaap	Stock Issued During Period Shares Stock Options Exercised StockIssuedDuringPeriodSharesStockOptionsExercised	2650000	shares
CY2019	us-gaap	Share Based Compensation Arrangements By Share Based Payment Award Options Exercises In Period Weighted Average Exercise Price ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice	2.45
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Forfeitures And Expirations In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod	807000	shares
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Forfeitures And Expirations In Period Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriodWeightedAverageExercisePrice	5.10
CY2019Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Number ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber	11269000	shares
CY2019Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice	4.68
CY2019	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Outstanding Weighted Average Remaining Contractual Term2 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2	P7Y3M18D
CY2019Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue	173471000	USD
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Gross ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross	252000	shares
CY2020	us-gaap	Share Based Compensation Arrangements By Share Based Payment Award Options Grants In Period Weighted Average Exercise Price ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice	12.96
CY2020	us-gaap	Stock Issued During Period Shares Stock Options Exercised StockIssuedDuringPeriodSharesStockOptionsExercised	4360000	shares
CY2020	us-gaap	Share Based Compensation Arrangements By Share Based Payment Award Options Exercises In Period Weighted Average Exercise Price ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice	3.46
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Forfeitures And Expirations In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod	198000	shares
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Forfeitures And Expirations In Period Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriodWeightedAverageExercisePrice	8.79
CY2020Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Number ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber	6963000	shares
CY2020Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice	5.63
CY2020	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Outstanding Weighted Average Remaining Contractual Term2 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2	P6Y8M12D
CY2020Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue	569094000	USD
CY2020Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Vested And Expected To Vest Exercisable Number ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableNumber	4214000	shares
CY2020Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Vested And Expected To Vest Exercisable Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageExercisePrice	3.71
CY2020	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Vested And Expected To Vest Exercisable Weighted Average Remaining Contractual Term1 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageRemainingContractualTerm1	P5Y9M18D
CY2020Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Vested And Expected To Vest Exercisable Aggregate Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableAggregateIntrinsicValue	352535000	USD
CY2020Q4	fsly	Share Based Compensation Arrangement By Share Based Payment Award Options Unvested Exercisable Number ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsUnvestedExercisableNumber	320000	shares
CY2020Q4	fsly	Share Based Compensation Arrangement By Share Based Payment Award Options Unvested Exercisable Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsUnvestedExercisableWeightedAverageExercisePrice	6.23
CY2020	fsly	Share Based Compensation Arrangement By Share Based Payment Award Options Unvested Exercisable Weighted Average Remaining Contractual Term ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsUnvestedExercisableWeightedAverageRemainingContractualTerm	P7Y8M12D
CY2020Q4	fsly	Share Based Compensation Arrangement By Share Based Payment Award Options Unvested Exercisable Aggregate Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsUnvestedExercisableAggregateIntrinsicValue	25973000	USD
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Exercises In Period Total Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue	200900000	USD
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Exercises In Period Total Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue	32600000	USD
CY2018	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Exercises In Period Total Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue	3000000.0	USD
CY2020	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Vested In Period Fair Value1 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1	10300000	USD
CY2019	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Vested In Period Fair Value1 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1	6100000	USD
CY2018	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Vested In Period Fair Value1 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1	3600000	USD
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue	86.77
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue	5.77
CY2018	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue	1.78
CY2020Q4	us-gaap	Employee Service Share Based Compensation Nonvested Awards Total Compensation Cost Not Yet Recognized Stock Options EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions	28600000	USD
CY2020Q4	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Nonvested Number Of Shares SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfShares	90977	shares
CY2019Q4	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Nonvested Number Of Shares SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfShares	199895	shares
CY2019Q4	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Nonvested Number Of Shares SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfShares	200000	shares
CY2018Q4	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Nonvested Number Of Shares SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfShares	245000	shares
CY2017Q4	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Nonvested Number Of Shares SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfShares	138000	shares
CY2020	fsly	Share Based Compensation Arrangement By Share Based Payment Award Options Nonvested Exercised Number Of Shares ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsNonvestedExercisedNumberOfShares	0	shares
CY2019	fsly	Share Based Compensation Arrangement By Share Based Payment Award Options Nonvested Exercised Number Of Shares ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsNonvestedExercisedNumberOfShares	117000	shares
CY2018	fsly	Share Based Compensation Arrangement By Share Based Payment Award Options Nonvested Exercised Number Of Shares ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsNonvestedExercisedNumberOfShares	238000	shares
CY2020	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Vested Number Of Shares SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedNumberOfShares	109000	shares
CY2019	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Vested Number Of Shares SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedNumberOfShares	162000	shares
CY2018	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Vested Number Of Shares SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedNumberOfShares	120000	shares
CY2020	fsly	Share Based Compensation Arrangement By Share Based Payment Award Options Nonvested Repurchased In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsNonvestedRepurchasedInPeriod	0	shares
CY2019	fsly	Share Based Compensation Arrangement By Share Based Payment Award Options Nonvested Repurchased In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsNonvestedRepurchasedInPeriod	0	shares
CY2018	fsly	Share Based Compensation Arrangement By Share Based Payment Award Options Nonvested Repurchased In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsNonvestedRepurchasedInPeriod	11000	shares
CY2020Q4	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Nonvested Number Of Shares SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfShares	91000	shares
CY2019Q4	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Nonvested Number Of Shares SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfShares	200000	shares
CY2018Q4	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Nonvested Number Of Shares SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfShares	245000	shares
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Forfeitures Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue
CY2020Q1	fsly	Number Of Shares Issued For Each Performance Based Stock Unit NumberOfSharesIssuedForEachPerformanceBasedStockUnit	1
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Dividend Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate	0
CY2020	fsly	Amount Withheld In Contributions For Employee Stock Purchase Plan AmountWithheldInContributionsForEmployeeStockPurchasePlan	9600000	USD
CY2019	fsly	Amount Withheld In Contributions For Employee Stock Purchase Plan AmountWithheldInContributionsForEmployeeStockPurchasePlan	5500000	USD
CY2020	us-gaap	Allocated Share Based Compensation Expense AllocatedShareBasedCompensationExpense	64433000	USD
CY2019	us-gaap	Allocated Share Based Compensation Expense AllocatedShareBasedCompensationExpense	12145000	USD
CY2018	us-gaap	Allocated Share Based Compensation Expense AllocatedShareBasedCompensationExpense	4079000	USD
CY2020	us-gaap	Employee Service Share Based Compensation Allocation Of Recognized Period Costs Capitalized Amount EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount	2000000.0	USD
CY2019	us-gaap	Employee Service Share Based Compensation Allocation Of Recognized Period Costs Capitalized Amount EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount	400000	USD
CY2018	us-gaap	Employee Service Share Based Compensation Allocation Of Recognized Period Costs Capitalized Amount EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount	0	USD
CY2020	us-gaap	Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	12471000	shares
CY2019	us-gaap	Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	13540000	shares
CY2020	us-gaap	Income Loss From Continuing Operations Before Income Taxes Domestic IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic	-86842000	USD
CY2019	us-gaap	Income Loss From Continuing Operations Before Income Taxes Domestic IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic	-30970000	USD
CY2018	us-gaap	Income Loss From Continuing Operations Before Income Taxes Domestic IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic	-20644000	USD
CY2020	us-gaap	Income Loss From Continuing Operations Before Income Taxes Foreign IncomeLossFromContinuingOperationsBeforeIncomeTaxesForeign	-20570000	USD
CY2019	us-gaap	Income Loss From Continuing Operations Before Income Taxes Foreign IncomeLossFromContinuingOperationsBeforeIncomeTaxesForeign	-20088000	USD
CY2018	us-gaap	Income Loss From Continuing Operations Before Income Taxes Foreign IncomeLossFromContinuingOperationsBeforeIncomeTaxesForeign	-10291000	USD
CY2020	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	-107412000	USD
CY2019	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	-51058000	USD
CY2020	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	0	USD
CY2019	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	0	USD
CY2018	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	0	USD
CY2020	us-gaap	Current State And Local Tax Expense Benefit CurrentStateAndLocalTaxExpenseBenefit	420000	USD
CY2019	us-gaap	Current State And Local Tax Expense Benefit CurrentStateAndLocalTaxExpenseBenefit	106000	USD
CY2018	us-gaap	Current State And Local Tax Expense Benefit CurrentStateAndLocalTaxExpenseBenefit	81000	USD
CY2020	us-gaap	Current Foreign Tax Expense Benefit CurrentForeignTaxExpenseBenefit	1050000	USD
CY2019	us-gaap	Current Foreign Tax Expense Benefit CurrentForeignTaxExpenseBenefit	386000	USD
CY2018	us-gaap	Current Foreign Tax Expense Benefit CurrentForeignTaxExpenseBenefit	104000	USD
CY2020	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	-10631000	USD
CY2019	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	0	USD
CY2018	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	0	USD
CY2020	us-gaap	Deferred State And Local Income Tax Expense Benefit DeferredStateAndLocalIncomeTaxExpenseBenefit	-2319000	USD
CY2019	us-gaap	Deferred State And Local Income Tax Expense Benefit DeferredStateAndLocalIncomeTaxExpenseBenefit	0	USD
CY2018	us-gaap	Deferred State And Local Income Tax Expense Benefit DeferredStateAndLocalIncomeTaxExpenseBenefit	0	USD
CY2020	us-gaap	Deferred Foreign Income Tax Expense Benefit DeferredForeignIncomeTaxExpenseBenefit	0	USD
CY2019	us-gaap	Deferred Foreign Income Tax Expense Benefit DeferredForeignIncomeTaxExpenseBenefit	0	USD
CY2018	us-gaap	Deferred Foreign Income Tax Expense Benefit DeferredForeignIncomeTaxExpenseBenefit	0	USD
CY2020	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	-11480000	USD
CY2019	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	492000	USD
CY2018	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	185000	USD
CY2020	us-gaap	Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	0.21
CY2019	us-gaap	Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	0.21
CY2018	us-gaap	Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	0.21
CY2020	us-gaap	Effective Income Tax Rate Reconciliation State And Local Income Taxes EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes	0.02
CY2019	us-gaap	Effective Income Tax Rate Reconciliation State And Local Income Taxes EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes	0
CY2018	us-gaap	Effective Income Tax Rate Reconciliation State And Local Income Taxes EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes	0
CY2020	us-gaap	Effective Income Tax Rate Reconciliation Change In Deferred Tax Assets Valuation Allowance EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance	-0.35
CY2019	us-gaap	Effective Income Tax Rate Reconciliation Change In Deferred Tax Assets Valuation Allowance EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance	-0.12
CY2018	us-gaap	Effective Income Tax Rate Reconciliation Change In Deferred Tax Assets Valuation Allowance EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance	-0.11
CY2020	us-gaap	Effective Income Tax Rate Reconciliation Foreign Income Tax Rate Differential EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential	-0.05
CY2019	us-gaap	Effective Income Tax Rate Reconciliation Foreign Income Tax Rate Differential EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential	-0.08
CY2018	us-gaap	Effective Income Tax Rate Reconciliation Foreign Income Tax Rate Differential EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential	-0.07
CY2020	fsly	Effective Income Tax Rate Reconciliation Acquisition Related Expenses Percent EffectiveIncomeTaxRateReconciliationAcquisitionRelatedExpensesPercent	-0.02
CY2019	fsly	Effective Income Tax Rate Reconciliation Acquisition Related Expenses Percent EffectiveIncomeTaxRateReconciliationAcquisitionRelatedExpensesPercent	0
CY2018	fsly	Effective Income Tax Rate Reconciliation Acquisition Related Expenses Percent EffectiveIncomeTaxRateReconciliationAcquisitionRelatedExpensesPercent	0
CY2020	us-gaap	Effective Income Tax Rate Reconciliation Nondeductible Expense Share Based Compensation Cost EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost	0.30
CY2019	us-gaap	Effective Income Tax Rate Reconciliation Nondeductible Expense Share Based Compensation Cost EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost	0
CY2018	us-gaap	Effective Income Tax Rate Reconciliation Nondeductible Expense Share Based Compensation Cost EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost	0
CY2020	us-gaap	Effective Income Tax Rate Reconciliation Other Adjustments EffectiveIncomeTaxRateReconciliationOtherAdjustments	0
CY2019	us-gaap	Effective Income Tax Rate Reconciliation Other Adjustments EffectiveIncomeTaxRateReconciliationOtherAdjustments	-0.02
CY2018	us-gaap	Effective Income Tax Rate Reconciliation Other Adjustments EffectiveIncomeTaxRateReconciliationOtherAdjustments	-0.04
CY2020	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	0.11
CY2019	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	-0.01
CY2018	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	-0.01
CY2020	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	-11500000	USD
CY2020	fsly	Income Tax Benefit Gross IncomeTaxBenefitGross	13000000.0	USD
CY2020Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals DeferredTaxAssetsTaxDeferredExpenseReservesAndAccruals	941000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals DeferredTaxAssetsTaxDeferredExpenseReservesAndAccruals	1839000	USD
CY2020Q4	fsly	Deferred Tax Asset Lease Liability DeferredTaxAssetLeaseLiability	17481000	USD
CY2019Q4	fsly	Deferred Tax Asset Lease Liability DeferredTaxAssetLeaseLiability	0	USD
CY2020Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Share Based Compensation Cost DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsShareBasedCompensationCost	3969000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Share Based Compensation Cost DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsShareBasedCompensationCost	1116000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Operating Loss Carryforwards DeferredTaxAssetsOperatingLossCarryforwards	109281000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Operating Loss Carryforwards DeferredTaxAssetsOperatingLossCarryforwards	30750000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Property Plant And Equipment DeferredTaxAssetsPropertyPlantAndEquipment	576000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Property Plant And Equipment DeferredTaxAssetsPropertyPlantAndEquipment	0	USD
CY2020Q4	us-gaap	Deferred Tax Assets Goodwill And Intangible Assets DeferredTaxAssetsGoodwillAndIntangibleAssets	0	USD
CY2019Q4	us-gaap	Deferred Tax Assets Goodwill And Intangible Assets DeferredTaxAssetsGoodwillAndIntangibleAssets	642000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Other DeferredTaxAssetsOther	0	USD
CY2019Q4	us-gaap	Deferred Tax Assets Other DeferredTaxAssetsOther	1753000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Gross DeferredTaxAssetsGross	132248000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Gross DeferredTaxAssetsGross	36100000	USD
CY2020Q4	us-gaap	Deferred Tax Liabilities Tax Deferred Income DeferredTaxLiabilitiesTaxDeferredIncome	673000	USD
CY2019Q4	us-gaap	Deferred Tax Liabilities Tax Deferred Income DeferredTaxLiabilitiesTaxDeferredIncome	0	USD
CY2020Q4	us-gaap	Deferred Tax Liabilities Leasing Arrangements DeferredTaxLiabilitiesLeasingArrangements	16160000	USD
CY2019Q4	us-gaap	Deferred Tax Liabilities Leasing Arrangements DeferredTaxLiabilitiesLeasingArrangements	0	USD
CY2020Q4	us-gaap	Deferred Tax Liabilities Property Plant And Equipment DeferredTaxLiabilitiesPropertyPlantAndEquipment	0	USD
CY2019Q4	us-gaap	Deferred Tax Liabilities Property Plant And Equipment DeferredTaxLiabilitiesPropertyPlantAndEquipment	285000	USD
CY2020Q4	us-gaap	Deferred Tax Liabilities Goodwill And Intangible Assets DeferredTaxLiabilitiesGoodwillAndIntangibleAssets	31188000	USD
CY2019Q4	us-gaap	Deferred Tax Liabilities Goodwill And Intangible Assets DeferredTaxLiabilitiesGoodwillAndIntangibleAssets	0	USD
CY2020Q4	fsly	Deferred Tax Liabilities State Taxes DeferredTaxLiabilitiesStateTaxes	4319000	USD
CY2019Q4	fsly	Deferred Tax Liabilities State Taxes DeferredTaxLiabilitiesStateTaxes	2034000	USD
CY2020Q4	us-gaap	Deferred Tax Liabilities Other DeferredTaxLiabilitiesOther	133000	USD
CY2019Q4	us-gaap	Deferred Tax Liabilities Other DeferredTaxLiabilitiesOther	0	USD
CY2020Q4	us-gaap	Deferred Income Tax Liabilities DeferredIncomeTaxLiabilities	52473000	USD
CY2019Q4	us-gaap	Deferred Income Tax Liabilities DeferredIncomeTaxLiabilities	2319000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Valuation Allowance DeferredTaxAssetsValuationAllowance	80028000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Valuation Allowance DeferredTaxAssetsValuationAllowance	33781000	USD
CY2020Q4	us-gaap	Deferred Tax Liabilities DeferredTaxLiabilities	253000	USD
CY2019Q4	us-gaap	Deferred Tax Liabilities DeferredTaxLiabilities	0	USD
CY2020	us-gaap	Valuation Allowance Deferred Tax Asset Change In Amount ValuationAllowanceDeferredTaxAssetChangeInAmount	46200000	USD
CY2019Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	0	USD
CY2018Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	0	USD
CY2020	us-gaap	Unrecognized Tax Benefits Increases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions	2328000	USD
CY2019	us-gaap	Unrecognized Tax Benefits Increases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions	0	USD
CY2020	us-gaap	Unrecognized Tax Benefits Increases Resulting From Current Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions	858000	USD
CY2019	us-gaap	Unrecognized Tax Benefits Increases Resulting From Current Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions	0	USD
CY2020Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	3186000	USD
CY2019Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	0	USD
CY2020Q4	us-gaap	Unrecognized Tax Benefits That Would Impact Effective Tax Rate UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate	3000000.0	USD
CY2020Q4	fsly	Accrued Payroll Taxes Cares Act AccruedPayrollTaxesCARESAct	3400000	USD
CY2020	us-gaap	Number Of Reportable Segments NumberOfReportableSegments	1	segment
CY2020Q4	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	95979000	USD
CY2019Q4	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	60037000	USD

Files In Submission

Name	View Source	Status
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0001517413-21-000030-index.html	Edgar Link	pending
0001517413-21-000030.txt	Edgar Link	pending
0001517413-21-000030-xbrl.zip	Edgar Link	pending
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Financial_Report.xlsx	Edgar Link	pending
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fsly-123119x10kex322.htm	Edgar Link	pending
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image_01.jpg	Edgar Link	pending
MetaLinks.json	Edgar Link	pending
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report.css	Edgar Link	pending
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$FSLY
Fastly Inc Stock $fsly

2019 Q4 Form 10-K Financial Statement

#000151741321000030 Filed on March 01, 2021

Income Statement

Balance Sheet

Cashflow Statement

Facts In Submission

Files In Submission

$FSLY Fastly Inc Stock $fsly

2019 Q4 Form 10-K Financial Statement

#000151741321000030 Filed on March 01, 2021

Income Statement

Balance Sheet

Cashflow Statement

Facts In Submission

Files In Submission

$FSLY
Fastly Inc Stock $fsly