$FSLY
Fastly Inc Stock $fsly

$fsly Overview Financials Valuation SEC Filings Company Website

2021 Q4 Form 10-Q Financial Statement

#000151741321000195 Filed on November 08, 2021

Income Statement

Concept	2021 Q4	2021 Q3	2020 Q3
Revenue	$97.72M	$86.74M	$70.64M
YoY Change	18.23%	22.79%	41.85%
Cost Of Revenue	$47.94M	$41.24M	$29.29M
YoY Change	42.06%	40.8%	31.4%
Gross Profit	$49.77M	$45.49M	$41.35M
YoY Change	1.79%	10.03%	50.32%
Gross Profit Margin	50.94%	52.45%	58.53%
Selling, General & Admin	$69.73M	$67.90M	$46.53M
YoY Change	3.69%	45.92%	65.33%
% of Gross Profit	140.1%	149.25%	112.54%
Research & Development	$35.00M	$32.53M	$18.27M
YoY Change	36.76%	78.03%	50.74%
% of Gross Profit	70.31%	71.5%	44.19%
Depreciation & Amortization	$13.40M	$7.400M	$4.900M
YoY Change	25.8%	51.02%	22.5%
% of Gross Profit	26.92%	16.27%	11.85%
Operating Expenses	$106.4M	$100.4M	$64.80M
YoY Change	13.29%	54.98%	60.94%
Operating Profit	-$56.66M	-$54.93M	-$23.45M
YoY Change	25.79%	134.22%	83.82%
Interest Expense	-$1.041M	$1.555M	$410.0K
YoY Change	285.56%	279.27%	-33.98%
% of Operating Profit
Other Income/Expense, Net	$201.0K	$41.00K	$69.00K
YoY Change	-128.71%	-40.58%	-36.7%
Pretax Income	-$57.50M	-$56.17M	-$23.44M
YoY Change	-1.41%	139.6%	93.46%
Income Tax	$25.00K	$30.00K	$300.0K
% Of Pretax Income
Net Earnings	-$57.52M	-$56.20M	-$23.78M
YoY Change	25.87%	136.34%	95.49%
Net Earnings / Revenue	-58.86%	-64.79%	-33.66%
Basic Earnings Per Share		-$0.48	-$0.22
Diluted Earnings Per Share	-$486.4K	-$0.48	-$0.22
COMMON SHARES
Basic Shares Outstanding	117.5M shares	116.5M shares	105.9M shares
Diluted Shares Outstanding		116.5M shares	105.9M shares

Balance Sheet

Concept	2021 Q4	2021 Q3	2020 Q3
SHORT-TERM ASSETS
Cash & Short-Term Investments	$527.9M	$643.4M	$402.3M
YoY Change	171.84%	59.95%	93.58%
Cash & Equivalents	$166.1M	$282.1M	$310.0M
Short-Term Investments	$361.8M	$361.3M	$92.30M
Other Short-Term Assets	$32.16M	$22.23M	$84.90M
YoY Change	91.43%	-73.82%	497.89%
Inventory
Prepaid Expenses
Receivables	$64.63M	$54.23M	$42.59M
Other Receivables	$0.00	$0.00	$0.00
Total Short-Term Assets	$624.6M	$719.9M	$529.7M
YoY Change	139.09%	35.9%	106.98%
LONG-TERM ASSETS
Property, Plant & Equipment	$167.0M	$147.7M	$83.50M
YoY Change	73.96%	76.93%	47.42%
Goodwill	$636.8M	$635.6M	$362.0K
YoY Change	0.19%	175489.78%	4.02%
Intangibles	$102.6M	$107.9M	$2.792M
YoY Change	-15.73%	3764.79%	140.48%
Long-Term Investments	$528.9M	$429.5M
YoY Change
Other Assets	$29.47M	$28.14M	$15.15M
YoY Change	18.26%	85.79%	14.41%
Total Long-Term Assets	$1.534B	$1.419B	$101.8M
YoY Change	60.05%	1293.97%	42.6%
TOTAL ASSETS
Total Short-Term Assets	$624.6M	$719.9M	$529.7M
Total Long-Term Assets	$1.534B	$1.419B	$101.8M
Total Assets	$2.159B	$2.139B	$631.5M
YoY Change	76.98%	238.7%	92.94%
SHORT-TERM LIABILITIES
YoY Change
Accounts Payable	$9.257M	$7.766M	$12.27M
YoY Change	1.17%	-36.72%	80.59%
Accrued Expenses	$36.11M	$36.06M	$38.56M
YoY Change	5.18%	-6.47%	64.33%
Deferred Revenue	$26.42M	$21.63M	$42.00K
YoY Change	66.0%	51402.38%
Short-Term Debt	$0.00	$0.00	$0.00
YoY Change
Long-Term Debt Due	$0.00	$18.68M	$6.060M
YoY Change	-100.0%	208.17%	-55.13%
Total Short-Term Liabilities	$131.9M	$107.3M	$66.45M
YoY Change	40.16%	61.44%	46.43%
LONG-TERM LIABILITIES
Long-Term Debt	$933.2M	$932.3M	$26.01M
YoY Change		3484.82%	67.3%
Other Long-Term Liabilities	$2.583M	$5.056M	$3.944M
YoY Change	-41.3%	28.19%	-43.52%
Total Long-Term Liabilities	$935.8M	$937.4M	$29.95M
YoY Change	21167.91%	3029.65%	32.95%
TOTAL LIABILITIES
Total Short-Term Liabilities	$131.9M	$107.3M	$66.45M
Total Long-Term Liabilities	$935.8M	$937.4M	$29.95M
Total Liabilities	$1.145B	$1.123B	$96.40M
YoY Change	624.33%	1065.33%	41.96%
SHAREHOLDERS EQUITY
Retained Earnings	-$510.9M	-$453.4M	-$242.2M
YoY Change	77.27%	87.16%	36.14%
Common Stock	$2.000K	$2.000K	$2.000K
YoY Change	0.0%	0.0%	0.0%
Preferred Stock
YoY Change
Treasury Stock (at cost)
YoY Change
Treasury Stock Shares
Shareholders Equity	$1.014B	$1.016B	$534.9M
YoY Change
Total Liabilities & Shareholders Equity	$2.159B	$2.139B	$631.5M
YoY Change	76.98%	238.7%	92.94%

Cashflow Statement

Concept	2021 Q4	2021 Q3	2020 Q3
OPERATING ACTIVITIES
Net Income	-$57.52M	-$56.20M	-$23.78M
YoY Change	25.87%	136.34%	95.49%
Depreciation, Depletion And Amortization	$13.40M	$7.400M	$4.900M
YoY Change	25.8%	51.02%	22.5%
Cash From Operating Activities	-$7.908M	-$2.691M	$27.20M
YoY Change	-74.61%	-109.89%	-316.04%
INVESTING ACTIVITIES
Capital Expenditures	-$6.729M	-$27.87M	-$13.80M
YoY Change	-6.15%	101.97%	215.07%
Acquisitions
YoY Change
Other Investing Activities	-$103.9M	-$376.1M	$34.04M
YoY Change	-60.06%	-1204.79%	-128.16%
Cash From Investing Activities	-$110.7M	-$403.9M	$20.24M
YoY Change	-58.62%	-2095.77%	-116.16%
FINANCING ACTIVITIES
Cash Dividend Paid
YoY Change
Common Stock Issuance & Retirement, Net
YoY Change
Debt Paid & Issued, Net
YoY Change
Cash From Financing Activities	2.603M	934.0K	5.190M
YoY Change	-114.81%	-82.0%	-124.82%
NET CHANGE
Cash From Operating Activities	-7.908M	-2.691M	27.20M
Cash From Investing Activities	-110.7M	-403.9M	20.24M
Cash From Financing Activities	2.603M	934.0K	5.190M
Net Change In Cash	-116.0M	-405.7M	52.63M
YoY Change	-63.32%	-870.85%	-133.15%
FREE CASH FLOW
Cash From Operating Activities	-$7.908M	-$2.691M	$27.20M
Capital Expenditures	-$6.729M	-$27.87M	-$13.80M
Free Cash Flow	-$1.179M	$25.18M	$41.00M
YoY Change	-95.08%	-38.58%	-599.39%

Facts In Submission

Frame	Concept Type	Concept / XBRL Key	Value	Unit
	dei	Entity Central Index Key EntityCentralIndexKey	0001517413
	dei	Current Fiscal Year End Date CurrentFiscalYearEndDate	--12-31
	dei	Document Fiscal Year Focus DocumentFiscalYearFocus	2021
	dei	Document Fiscal Period Focus DocumentFiscalPeriodFocus	Q3
	dei	Amendment Flag AmendmentFlag	false
	dei	Document Type DocumentType	10-Q
	dei	Document Quarterly Report DocumentQuarterlyReport	true
	dei	Document Period End Date DocumentPeriodEndDate	2021-09-30
	dei	Document Transition Report DocumentTransitionReport	false
	dei	Entity File Number EntityFileNumber	001-38897
	dei	Entity Registrant Name EntityRegistrantName	FASTLY, INC.
	dei	Entity Incorporation State Country Code EntityIncorporationStateCountryCode	DE
	dei	Entity Tax Identification Number EntityTaxIdentificationNumber	27-5411834
	dei	Entity Address Address Line1 EntityAddressAddressLine1	475 Brannan Street, Suite 300
	dei	Entity Address City Or Town EntityAddressCityOrTown	San Francisco
	dei	Entity Address State Or Province EntityAddressStateOrProvince	CA
	dei	Entity Address Postal Zip Code EntityAddressPostalZipCode	94107
	dei	City Area Code CityAreaCode	844
	dei	Local Phone Number LocalPhoneNumber	432-7859
	dei	Security12b Title Security12bTitle	Class A Common Stock, $0.00002 par value
	dei	Trading Symbol TradingSymbol	FSLY
	dei	Security Exchange Name SecurityExchangeName	NYSE
	dei	Entity Current Reporting Status EntityCurrentReportingStatus	Yes
	dei	Entity Interactive Data Current EntityInteractiveDataCurrent	Yes
	dei	Entity Filer Category EntityFilerCategory	Large Accelerated Filer
	dei	Entity Small Business EntitySmallBusiness	false
	dei	Entity Emerging Growth Company EntityEmergingGrowthCompany	false
	dei	Entity Shell Company EntityShellCompany	false
CY2021Q4	dei	Entity Common Stock Shares Outstanding EntityCommonStockSharesOutstanding	117500000	shares
CY2021Q3	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	282131000	USD
CY2020Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	62900000	USD
CY2021Q3	us-gaap	Available For Sale Securities Debt Securities Current AvailableForSaleSecuritiesDebtSecuritiesCurrent	361290000	USD
CY2020Q4	us-gaap	Available For Sale Securities Debt Securities Current AvailableForSaleSecuritiesDebtSecuritiesCurrent	131283000	USD
CY2021Q3	us-gaap	Allowance For Doubtful Accounts Receivable Current AllowanceForDoubtfulAccountsReceivableCurrent	3173000	USD
CY2020Q4	us-gaap	Allowance For Doubtful Accounts Receivable Current AllowanceForDoubtfulAccountsReceivableCurrent	3248000	USD
CY2021Q3	us-gaap	Accounts Receivable Net Current AccountsReceivableNetCurrent	54234000	USD
CY2020Q4	us-gaap	Accounts Receivable Net Current AccountsReceivableNetCurrent	50258000	USD
CY2021Q3	us-gaap	Gross Profit GrossProfit	45491000	USD
CY2020Q3	us-gaap	Gross Profit GrossProfit	41346000	USD
	us-gaap	Gross Profit GrossProfit	137555000	USD
	us-gaap	Gross Profit GrossProfit	121971000	USD
CY2021Q3	us-gaap	Research And Development Expense ResearchAndDevelopmentExpense	32528000	USD
CY2020Q3	us-gaap	Research And Development Expense ResearchAndDevelopmentExpense	18271000	USD
	us-gaap	Research And Development Expense ResearchAndDevelopmentExpense	91862000	USD
	us-gaap	Research And Development Expense ResearchAndDevelopmentExpense	49224000	USD
CY2021Q3	us-gaap	Selling And Marketing Expense SellingAndMarketingExpense	39288000	USD
CY2020Q3	us-gaap	Selling And Marketing Expense SellingAndMarketingExpense	22568000	USD
	us-gaap	Selling And Marketing Expense SellingAndMarketingExpense	110494000	USD
	us-gaap	Selling And Marketing Expense SellingAndMarketingExpense	66416000	USD
CY2021Q3	us-gaap	Restricted Cash And Cash Equivalents At Carrying Value RestrictedCashAndCashEquivalentsAtCarryingValue	0	USD
CY2020Q4	us-gaap	Restricted Cash And Cash Equivalents At Carrying Value RestrictedCashAndCashEquivalentsAtCarryingValue	87000	USD
CY2021Q3	us-gaap	Prepaid Expense And Other Assets Current PrepaidExpenseAndOtherAssetsCurrent	22230000	USD
CY2020Q4	us-gaap	Prepaid Expense And Other Assets Current PrepaidExpenseAndOtherAssetsCurrent	16728000	USD
CY2021Q3	us-gaap	Assets Current AssetsCurrent	719885000	USD
CY2020Q4	us-gaap	Assets Current AssetsCurrent	261256000	USD
CY2021Q3	us-gaap	Available For Sale Securities Debt Securities Noncurrent AvailableForSaleSecuritiesDebtSecuritiesNoncurrent	429489000	USD
CY2020Q4	us-gaap	Available For Sale Securities Debt Securities Noncurrent AvailableForSaleSecuritiesDebtSecuritiesNoncurrent	20448000	USD
CY2021Q3	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	147729000	USD
CY2020Q4	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	95979000	USD
CY2021Q3	us-gaap	Operating Lease Right Of Use Asset OperatingLeaseRightOfUseAsset	70149000	USD
CY2020Q4	us-gaap	Operating Lease Right Of Use Asset OperatingLeaseRightOfUseAsset	60019000	USD
CY2021Q3	us-gaap	Goodwill Goodwill	635635000	USD
CY2020Q4	us-gaap	Goodwill Goodwill	635590000	USD
CY2021Q3	us-gaap	Intangible Assets Net Excluding Goodwill IntangibleAssetsNetExcludingGoodwill	107905000	USD
CY2020Q4	us-gaap	Intangible Assets Net Excluding Goodwill IntangibleAssetsNetExcludingGoodwill	121742000	USD
CY2021Q3	us-gaap	Other Assets Noncurrent OtherAssetsNoncurrent	28142000	USD
CY2020Q4	us-gaap	Other Assets Noncurrent OtherAssetsNoncurrent	24917000	USD
CY2021Q3	us-gaap	Assets Assets	2138934000	USD
CY2020Q4	us-gaap	Assets Assets	1219951000	USD
CY2021Q3	us-gaap	Accounts Payable Current AccountsPayableCurrent	7766000	USD
CY2020Q4	us-gaap	Accounts Payable Current AccountsPayableCurrent	9150000	USD
CY2021Q3	us-gaap	Accrued Liabilities Current AccruedLiabilitiesCurrent	36063000	USD
CY2020Q4	us-gaap	Accrued Liabilities Current AccruedLiabilitiesCurrent	34334000	USD
CY2021Q3	us-gaap	Finance Lease Liability Current FinanceLeaseLiabilityCurrent	18675000	USD
CY2020Q4	us-gaap	Finance Lease Liability Current FinanceLeaseLiabilityCurrent	11033000	USD
CY2021Q3	us-gaap	Operating Lease Liability Current OperatingLeaseLiabilityCurrent	20007000	USD
CY2020Q4	us-gaap	Operating Lease Liability Current OperatingLeaseLiabilityCurrent	19895000	USD
CY2021Q3	us-gaap	Other Liabilities Current OtherLiabilitiesCurrent	24758000	USD
CY2020Q4	us-gaap	Other Liabilities Current OtherLiabilitiesCurrent	19677000	USD
CY2021Q3	us-gaap	Liabilities Current LiabilitiesCurrent	107269000	USD
CY2020Q4	us-gaap	Liabilities Current LiabilitiesCurrent	94089000	USD
CY2021Q3	us-gaap	Long Term Debt Noncurrent LongTermDebtNoncurrent	932305000	USD
CY2020Q4	us-gaap	Long Term Debt Noncurrent LongTermDebtNoncurrent	0	USD
CY2021Q3	us-gaap	Finance Lease Liability Noncurrent FinanceLeaseLiabilityNoncurrent	24659000	USD
CY2020Q4	us-gaap	Finance Lease Liability Noncurrent FinanceLeaseLiabilityNoncurrent	14707000	USD
CY2021Q3	us-gaap	Operating Lease Liability Noncurrent OperatingLeaseLiabilityNoncurrent	54066000	USD
CY2020Q4	us-gaap	Operating Lease Liability Noncurrent OperatingLeaseLiabilityNoncurrent	44890000	USD
CY2021Q3	us-gaap	Other Liabilities Noncurrent OtherLiabilitiesNoncurrent	5056000	USD
CY2020Q4	us-gaap	Other Liabilities Noncurrent OtherLiabilitiesNoncurrent	4400000	USD
CY2021Q3	us-gaap	Liabilities Liabilities	1123355000	USD
CY2020Q4	us-gaap	Liabilities Liabilities	158086000	USD
CY2021Q3	us-gaap	Commitments And Contingencies CommitmentsAndContingencies		USD
CY2020Q4	us-gaap	Commitments And Contingencies CommitmentsAndContingencies		USD
CY2021Q3	us-gaap	Common Stock Value CommonStockValue	2000	USD
CY2020Q4	us-gaap	Common Stock Value CommonStockValue	2000	USD
CY2021Q3	us-gaap	Additional Paid In Capital AdditionalPaidInCapital	1469366000	USD
CY2020Q4	us-gaap	Additional Paid In Capital AdditionalPaidInCapital	1350050000	USD
CY2021Q3	us-gaap	General And Administrative Expense GeneralAndAdministrativeExpense	28609000	USD
CY2020Q3	us-gaap	General And Administrative Expense GeneralAndAdministrativeExpense	23961000	USD
	us-gaap	General And Administrative Expense GeneralAndAdministrativeExpense	97564000	USD
	us-gaap	General And Administrative Expense GeneralAndAdministrativeExpense	56199000	USD
CY2021Q3	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	-420000	USD
CY2020Q4	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	6000	USD
CY2021Q3	us-gaap	Retained Earnings Accumulated Deficit RetainedEarningsAccumulatedDeficit	-453369000	USD
CY2020Q4	us-gaap	Retained Earnings Accumulated Deficit RetainedEarningsAccumulatedDeficit	-288193000	USD
CY2021Q3	us-gaap	Stockholders Equity StockholdersEquity	1015579000	USD
CY2020Q4	us-gaap	Stockholders Equity StockholdersEquity	1061865000	USD
CY2021Q3	us-gaap	Liabilities And Stockholders Equity LiabilitiesAndStockholdersEquity	2138934000	USD
CY2020Q4	us-gaap	Liabilities And Stockholders Equity LiabilitiesAndStockholdersEquity	1219951000	USD
CY2021Q3	us-gaap	Revenue From Contract With Customer Including Assessed Tax RevenueFromContractWithCustomerIncludingAssessedTax	86735000	USD
CY2020Q3	us-gaap	Revenue From Contract With Customer Including Assessed Tax RevenueFromContractWithCustomerIncludingAssessedTax	70638000	USD
	us-gaap	Revenue From Contract With Customer Including Assessed Tax RevenueFromContractWithCustomerIncludingAssessedTax	256613000	USD
	us-gaap	Revenue From Contract With Customer Including Assessed Tax RevenueFromContractWithCustomerIncludingAssessedTax	208225000	USD
CY2021Q3	us-gaap	Cost Of Revenue CostOfRevenue	41244000	USD
CY2020Q3	us-gaap	Cost Of Revenue CostOfRevenue	29292000	USD
	us-gaap	Cost Of Revenue CostOfRevenue	119058000	USD
	us-gaap	Cost Of Revenue CostOfRevenue	86254000	USD
CY2021Q3	us-gaap	Operating Expenses OperatingExpenses	100425000	USD
CY2020Q3	us-gaap	Operating Expenses OperatingExpenses	64800000	USD
	us-gaap	Operating Expenses OperatingExpenses	299920000	USD
	us-gaap	Operating Expenses OperatingExpenses	171839000	USD
CY2021Q3	us-gaap	Operating Income Loss OperatingIncomeLoss	-54934000	USD
CY2020Q3	us-gaap	Operating Income Loss OperatingIncomeLoss	-23454000	USD
	us-gaap	Operating Income Loss OperatingIncomeLoss	-162365000	USD
	us-gaap	Operating Income Loss OperatingIncomeLoss	-49868000	USD
CY2021Q3	us-gaap	Investment Income Interest InvestmentIncomeInterest	280000	USD
CY2020Q3	us-gaap	Investment Income Interest InvestmentIncomeInterest	353000	USD
	us-gaap	Investment Income Interest InvestmentIncomeInterest	730000	USD
	us-gaap	Investment Income Interest InvestmentIncomeInterest	1450000	USD
CY2021Q3	us-gaap	Interest Expense InterestExpense	1555000	USD
CY2020Q3	us-gaap	Interest Expense InterestExpense	410000	USD
	us-gaap	Interest Expense InterestExpense	3652000	USD
	us-gaap	Interest Expense InterestExpense	1097000	USD
CY2021Q3	us-gaap	Other Nonoperating Income Expense OtherNonoperatingIncomeExpense	41000	USD
CY2020Q3	us-gaap	Other Nonoperating Income Expense OtherNonoperatingIncomeExpense	69000	USD
	us-gaap	Other Nonoperating Income Expense OtherNonoperatingIncomeExpense	155000	USD
	us-gaap	Other Nonoperating Income Expense OtherNonoperatingIncomeExpense	418000	USD
CY2021Q3	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	-56168000	USD
CY2020Q3	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	-23442000	USD
	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	-165132000	USD
	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	-49097000	USD
CY2021Q3	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	30000	USD
CY2020Q3	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	336000	USD
	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	44000	USD
	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	1131000	USD
CY2021Q3	us-gaap	Net Income Loss NetIncomeLoss	-56198000	USD
CY2020Q3	us-gaap	Net Income Loss NetIncomeLoss	-23778000	USD
CY2020Q3	us-gaap	Net Income Loss NetIncomeLoss	-23778000	USD
	us-gaap	Net Income Loss NetIncomeLoss	-165176000	USD
	us-gaap	Net Income Loss NetIncomeLoss	-50228000	USD
	us-gaap	Net Income Loss NetIncomeLoss	-50228000	USD
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CY2020Q3	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	-0.22
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	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	-1.43
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	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	-0.50
	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	-0.50
CY2021Q3	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	116475000	shares
CY2021Q3	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	116475000	shares
CY2020Q3	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	105942000	shares
CY2020Q3	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	105942000	shares
	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	115320000	shares
	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	115320000	shares
	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	100413000	shares
	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	100413000	shares
CY2021Q3	us-gaap	Net Income Loss NetIncomeLoss	-56198000	USD
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	us-gaap	Net Income Loss NetIncomeLoss	-165176000	USD
	us-gaap	Net Income Loss NetIncomeLoss	-50228000	USD
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	us-gaap	Other Comprehensive Income Foreign Currency Transaction And Translation Adjustment Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent	-228000	USD
	us-gaap	Other Comprehensive Income Foreign Currency Transaction And Translation Adjustment Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent	-149000	USD
CY2021Q3	us-gaap	Other Comprehensive Income Availableforsale Securities Adjustment Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeAvailableforsaleSecuritiesAdjustmentNetOfTaxPortionAttributableToParent	27000	USD
CY2020Q3	us-gaap	Other Comprehensive Income Availableforsale Securities Adjustment Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeAvailableforsaleSecuritiesAdjustmentNetOfTaxPortionAttributableToParent	-193000	USD
	us-gaap	Other Comprehensive Income Availableforsale Securities Adjustment Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeAvailableforsaleSecuritiesAdjustmentNetOfTaxPortionAttributableToParent	-198000	USD
	us-gaap	Other Comprehensive Income Availableforsale Securities Adjustment Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeAvailableforsaleSecuritiesAdjustmentNetOfTaxPortionAttributableToParent	77000	USD
CY2021Q3	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent	-159000	USD
CY2020Q3	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent	-261000	USD
	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent	-426000	USD
	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent	-72000	USD
CY2021Q3	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	-56357000	USD
CY2020Q3	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	-24039000	USD
	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	-165602000	USD
	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	-50300000	USD
CY2021Q2	us-gaap	Stockholders Equity StockholdersEquity	1029090000	USD
CY2021Q3	us-gaap	Stock Issued During Period Value Stock Options Exercised StockIssuedDuringPeriodValueStockOptionsExercised	3489000	USD
CY2021Q3	fsly	Stock Issued During Period Value Vesting Of Early Exercised Stock Options StockIssuedDuringPeriodValueVestingOfEarlyExercisedStockOptions	64000	USD
CY2021Q3	us-gaap	Adjustments To Additional Paid In Capital Sharebased Compensation Requisite Service Period Recognition Value AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue	39293000	USD
CY2021Q3	us-gaap	Net Income Loss NetIncomeLoss	-56198000	USD
CY2021Q3	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent	-159000	USD
CY2021Q3	us-gaap	Stockholders Equity StockholdersEquity	1015579000	USD
CY2020Q2	us-gaap	Stockholders Equity StockholdersEquity	541913000	USD
CY2020Q3	fsly	Stock Issued During Period Value Vesting Of Early Exercised Stock Options StockIssuedDuringPeriodValueVestingOfEarlyExercisedStockOptions	127000	USD
CY2020Q3	us-gaap	Stock Issued During Period Value Stock Options Exercised StockIssuedDuringPeriodValueStockOptionsExercised	4122000	USD
CY2020Q3	us-gaap	Adjustments To Additional Paid In Capital Sharebased Compensation Requisite Service Period Recognition Value AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue	12745000	USD
CY2020Q3	us-gaap	Net Income Loss NetIncomeLoss	-23778000	USD
CY2020Q3	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent	-261000	USD
CY2020Q3	us-gaap	Stockholders Equity StockholdersEquity	534868000	USD
CY2020Q4	us-gaap	Stockholders Equity StockholdersEquity	1061865000	USD
	us-gaap	Stock Issued During Period Value Stock Options Exercised StockIssuedDuringPeriodValueStockOptionsExercised	9094000	USD
	fsly	Stock Issued During Period Value Vesting Of Early Exercised Stock Options StockIssuedDuringPeriodValueVestingOfEarlyExercisedStockOptions	192000	USD
	us-gaap	Stock Issued During Period Value Employee Stock Purchase Plan StockIssuedDuringPeriodValueEmployeeStockPurchasePlan	5719000	USD
	us-gaap	Adjustments To Additional Paid In Capital Sharebased Compensation Requisite Service Period Recognition Value AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue	104311000	USD
	us-gaap	Net Income Loss NetIncomeLoss	-165176000	USD
	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent	-426000	USD
CY2021Q3	us-gaap	Stockholders Equity StockholdersEquity	1015579000	USD
CY2019Q4	us-gaap	Stockholders Equity StockholdersEquity	257652000	USD
	us-gaap	Stock Issued During Period Value New Issues StockIssuedDuringPeriodValueNewIssues	274177000	USD
	fsly	Stock Issued During Period Value Vesting Of Early Exercised Stock Options StockIssuedDuringPeriodValueVestingOfEarlyExercisedStockOptions	401000	USD
	us-gaap	Stock Issued During Period Value Employee Stock Purchase Plan StockIssuedDuringPeriodValueEmployeeStockPurchasePlan	4247000	USD
	us-gaap	Stock Issued During Period Value Stock Options Exercised StockIssuedDuringPeriodValueStockOptionsExercised	12953000	USD
	us-gaap	Adjustments To Additional Paid In Capital Sharebased Compensation Requisite Service Period Recognition Value AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue	35990000	USD
	us-gaap	Net Income Loss NetIncomeLoss	-50228000	USD
	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent	-72000	USD
CY2020Q3	us-gaap	Stockholders Equity StockholdersEquity	534868000	USD
	us-gaap	Net Income Loss NetIncomeLoss	-165176000	USD
	us-gaap	Net Income Loss NetIncomeLoss	-50228000	USD
	us-gaap	Depreciation Nonproduction DepreciationNonproduction	20710000	USD
	us-gaap	Depreciation Nonproduction DepreciationNonproduction	14266000	USD
	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	15929000	USD
	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	145000	USD
	fsly	Amortization Of Right Of Use Assets And Other AmortizationOfRightOfUseAssetsAndOther	19818000	USD
	fsly	Amortization Of Right Of Use Assets And Other AmortizationOfRightOfUseAssetsAndOther	15824000	USD
	us-gaap	Amortization Of Financing Costs And Discounts AmortizationOfFinancingCostsAndDiscounts	2235000	USD
	us-gaap	Amortization Of Financing Costs And Discounts AmortizationOfFinancingCostsAndDiscounts	58000	USD
	us-gaap	Capitalized Contract Cost Amortization CapitalizedContractCostAmortization	4567000	USD
	us-gaap	Capitalized Contract Cost Amortization CapitalizedContractCostAmortization	2375000	USD
	us-gaap	Share Based Compensation ShareBasedCompensation	100900000	USD
	us-gaap	Share Based Compensation ShareBasedCompensation	34752000	USD
	us-gaap	Provision For Doubtful Accounts ProvisionForDoubtfulAccounts	41000	USD
	us-gaap	Provision For Doubtful Accounts ProvisionForDoubtfulAccounts	1212000	USD
	us-gaap	Finance Lease Interest Payment On Liability FinanceLeaseInterestPaymentOnLiability	1259000	USD
	us-gaap	Finance Lease Interest Payment On Liability FinanceLeaseInterestPaymentOnLiability	454000	USD
	us-gaap	Gain Loss On Sale Of Property Plant Equipment GainLossOnSaleOfPropertyPlantEquipment	177000	USD
	us-gaap	Gain Loss On Sale Of Property Plant Equipment GainLossOnSaleOfPropertyPlantEquipment	133000	USD
	us-gaap	Other Noncash Income Expense OtherNoncashIncomeExpense	-1496000	USD
	us-gaap	Other Noncash Income Expense OtherNoncashIncomeExpense	-176000	USD
	us-gaap	Increase Decrease In Accounts Receivable IncreaseDecreaseInAccountsReceivable	4017000	USD
	us-gaap	Increase Decrease In Accounts Receivable IncreaseDecreaseInAccountsReceivable	6669000	USD
	us-gaap	Increase Decrease In Prepaid Deferred Expense And Other Assets IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets	5502000	USD
	us-gaap	Increase Decrease In Prepaid Deferred Expense And Other Assets IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets	3778000	USD
	us-gaap	Increase Decrease In Other Operating Assets IncreaseDecreaseInOtherOperatingAssets	7320000	USD
	us-gaap	Increase Decrease In Other Operating Assets IncreaseDecreaseInOtherOperatingAssets	7410000	USD
	us-gaap	Increase Decrease In Accounts Payable IncreaseDecreaseInAccountsPayable	-1653000	USD
	us-gaap	Increase Decrease In Accounts Payable IncreaseDecreaseInAccountsPayable	7046000	USD
	us-gaap	Increase Decrease In Accrued Liabilities IncreaseDecreaseInAccruedLiabilities	2713000	USD
	us-gaap	Increase Decrease In Accrued Liabilities IncreaseDecreaseInAccruedLiabilities	17224000	USD
	fsly	Increase Decrease In Operating Lease Liabilities IncreaseDecreaseInOperatingLeaseLiabilities	-19735000	USD
	fsly	Increase Decrease In Operating Lease Liabilities IncreaseDecreaseInOperatingLeaseLiabilities	-12852000	USD
	us-gaap	Increase Decrease In Other Operating Liabilities IncreaseDecreaseInOtherOperatingLiabilities	5856000	USD
	us-gaap	Increase Decrease In Other Operating Liabilities IncreaseDecreaseInOtherOperatingLiabilities	-321000	USD
	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	-30574000	USD
	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	11233000	USD
	us-gaap	Payments To Acquire Short Term Investments PaymentsToAcquireShortTermInvestments	777569000	USD
	us-gaap	Payments To Acquire Short Term Investments PaymentsToAcquireShortTermInvestments	204361000	USD
	us-gaap	Proceeds From Sale And Maturity Of Available For Sale Securities ProceedsFromSaleAndMaturityOfAvailableForSaleSecurities	64236000	USD
	us-gaap	Proceeds From Sale And Maturity Of Available For Sale Securities ProceedsFromSaleAndMaturityOfAvailableForSaleSecurities	143241000	USD
	us-gaap	Proceeds From Sale And Maturity Of Marketable Securities ProceedsFromSaleAndMaturityOfMarketableSecurities	72853000	USD
	us-gaap	Proceeds From Sale And Maturity Of Marketable Securities ProceedsFromSaleAndMaturityOfMarketableSecurities	83718000	USD
	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	31267000	USD
	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	23602000	USD
	us-gaap	Proceeds From Sale Of Property Plant And Equipment ProceedsFromSaleOfPropertyPlantAndEquipment	291000	USD
	us-gaap	Proceeds From Sale Of Property Plant And Equipment ProceedsFromSaleOfPropertyPlantAndEquipment	150000	USD
	us-gaap	Payments For Software PaymentsForSoftware	10299000	USD
	us-gaap	Payments For Software PaymentsForSoftware	4082000	USD
	us-gaap	Payments To Acquire Intangible Assets PaymentsToAcquireIntangibleAssets	2092000	USD
	us-gaap	Payments To Acquire Intangible Assets PaymentsToAcquireIntangibleAssets	2092000	USD
	us-gaap	Payments To Acquire Intangible Assets PaymentsToAcquireIntangibleAssets	1811000	USD
	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-683847000	USD
	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-6747000	USD
	us-gaap	Proceeds From Issuance Of Common Stock ProceedsFromIssuanceOfCommonStock	0	USD
	us-gaap	Proceeds From Issuance Of Common Stock ProceedsFromIssuanceOfCommonStock	274896000	USD
	us-gaap	Payments Of Stock Issuance Costs PaymentsOfStockIssuanceCosts	0	USD
	us-gaap	Payments Of Stock Issuance Costs PaymentsOfStockIssuanceCosts	675000	USD
	us-gaap	Proceeds From Convertible Debt ProceedsFromConvertibleDebt	930775000	USD
	us-gaap	Proceeds From Convertible Debt ProceedsFromConvertibleDebt	0	USD
	us-gaap	Payments Of Debt Issuance Costs PaymentsOfDebtIssuanceCosts	1351000	USD
	us-gaap	Payments Of Debt Issuance Costs PaymentsOfDebtIssuanceCosts	0	USD
	us-gaap	Finance Lease Principal Payments FinanceLeasePrincipalPayments	10564000	USD
	us-gaap	Finance Lease Principal Payments FinanceLeasePrincipalPayments	3901000	USD
	us-gaap	Proceeds From Stock Plans ProceedsFromStockPlans	5994000	USD
	us-gaap	Proceeds From Stock Plans ProceedsFromStockPlans	6206000	USD
	us-gaap	Proceeds From Stock Options Exercised ProceedsFromStockOptionsExercised	9094000	USD
	us-gaap	Proceeds From Stock Options Exercised ProceedsFromStockOptionsExercised	12953000	USD
	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	933948000	USD
	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	289479000	USD
	us-gaap	Effect Of Exchange Rate On Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	-383000	USD
	us-gaap	Effect Of Exchange Rate On Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	-139000	USD
	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect	219144000	USD
	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect	293826000	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
CY2021Q3	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	283024000	USD
CY2020Q3	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	380055000	USD
	us-gaap	Interest Paid Net InterestPaidNet	1379000	USD
	us-gaap	Interest Paid Net InterestPaidNet	758000	USD
	us-gaap	Income Taxes Paid Net IncomeTaxesPaidNet	240000	USD
	us-gaap	Income Taxes Paid Net IncomeTaxesPaidNet	1000000	USD
	us-gaap	Capital Expenditures Incurred But Not Yet Paid CapitalExpendituresIncurredButNotYetPaid	443000	USD
	us-gaap	Capital Expenditures Incurred But Not Yet Paid CapitalExpendituresIncurredButNotYetPaid	9613000	USD
	fsly	Vestingof Early Exercised Stock Options VestingofEarlyExercisedStockOptions	192000	USD
	fsly	Vestingof Early Exercised Stock Options VestingofEarlyExercisedStockOptions	401000	USD
	fsly	Cashless Exercise Of Common Stock Warrants CashlessExerciseOfCommonStockWarrants	0	USD
	fsly	Cashless Exercise Of Common Stock Warrants CashlessExerciseOfCommonStockWarrants	1557000	USD
	us-gaap	Employee Service Share Based Compensation Allocation Of Recognized Period Costs Capitalized Amount EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount	3411000	USD
	us-gaap	Employee Service Share Based Compensation Allocation Of Recognized Period Costs Capitalized Amount EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount	1238000	USD
	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	25745000	USD
	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	15095000	USD
	us-gaap	Right Of Use Asset Obtained In Exchange For Finance Lease Liability RightOfUseAssetObtainedInExchangeForFinanceLeaseLiability	28399000	USD
	us-gaap	Right Of Use Asset Obtained In Exchange For Finance Lease Liability RightOfUseAssetObtainedInExchangeForFinanceLeaseLiability	11352000	USD
CY2021Q3	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	282131000	USD
CY2020Q3	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	309968000	USD
CY2021Q3	us-gaap	Restricted Cash And Cash Equivalents At Carrying Value RestrictedCashAndCashEquivalentsAtCarryingValue	0	USD
CY2020Q3	us-gaap	Restricted Cash And Cash Equivalents At Carrying Value RestrictedCashAndCashEquivalentsAtCarryingValue	70087000	USD
CY2021Q3	us-gaap	Restricted Cash And Cash Equivalents Noncurrent RestrictedCashAndCashEquivalentsNoncurrent	893000	USD
CY2020Q3	us-gaap	Restricted Cash And Cash Equivalents Noncurrent RestrictedCashAndCashEquivalentsNoncurrent	0	USD
CY2021Q3	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	283024000	USD
	us-gaap	Capitalized Contract Cost Amortization CapitalizedContractCostAmortization	2400000	USD
CY2020Q3	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	380055000	USD
	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. As of September 30, 2021, our edge network spans across 68 markets around the world. 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%">Conversion of dual class common stock structure</span></div><div style="margin-bottom:12pt;text-indent:36pt"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%">On October 12, 2020, the outstanding shares of our Class B common stock represented less than 10% of the aggregate number of shares of the then outstanding Class A common stock and Class B common stock. As a result, all outstanding shares of Class B common stock automatically converted into the same number of shares of Class A common stock on July 12, 2021, pursuant to the terms of our amended and restated certificate of incorporation (the "Certificate"). Upon the conversion, outstanding options denominated in shares of Class B common stock issued under any of our equity incentive plans remained unchanged, except that they now represent the right to receive shares of Class A common stock on exercise. In accordance with the Certificate, the shares of Class B common stock that converted to Class A common stock were retired and will not be reissued by us.</span></div>
CY2021Q3	fsly	Operating Markets OperatingMarkets	68	operatingMarket
CY2020Q2	us-gaap	Stockholders Equity StockholdersEquity	541913000	USD
CY2020Q3	us-gaap	Stockholders Equity StockholdersEquity	534868000	USD
CY2019Q4	us-gaap	Stockholders Equity StockholdersEquity	257652000	USD
CY2020Q3	us-gaap	Stockholders Equity StockholdersEquity	534868000	USD
	fsly	Amortization Of Deferred Rent AmortizationOfDeferredRent	0	USD
	fsly	Amortization Of Right Of Use Assets And Other AmortizationOfRightOfUseAssetsAndOther	15824000	USD
	us-gaap	Other Noncash Income Expense OtherNoncashIncomeExpense	-176000	USD
CY2021Q3	us-gaap	Revenue From Contract With Customer Including Assessed Tax RevenueFromContractWithCustomerIncludingAssessedTax	86735000	USD
	fsly	Increase Decrease In Operating Lease Liabilities IncreaseDecreaseInOperatingLeaseLiabilities	-12852000	USD
	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	11233000	USD
	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	23602000	USD
	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-6747000	USD
	us-gaap	Repayments Of Long Term Capital Lease Obligations RepaymentsOfLongTermCapitalLeaseObligations	0	USD
	us-gaap	Finance Lease Principal Payments FinanceLeasePrincipalPayments	3901000	USD
	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	289479000	USD
	us-gaap	Capital Lease Obligations Incurred CapitalLeaseObligationsIncurred	0	USD
	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	15095000	USD
	us-gaap	Right Of Use Asset Obtained In Exchange For Finance Lease Liability RightOfUseAssetObtainedInExchangeForFinanceLeaseLiability	11352000	USD
	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 condensed 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 including our goodwill and intangible 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 condensed 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 adversely impacted many operational aspects of our business and may continue to do so in the future. Since the start of the pandemic, we have assessed the impact that COVID-19 had on our results of operations, including, but not limited to an assessment of our allowance for credit losses, the carrying value of short-term and long-term marketable securities, the carrying value of goodwill and other long-lived assets, and the impact on revenue recognition and cost of revenues. The future impacts of the pandemic and any resulting economic impact are largely unknown and are continuing to evolve. 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>
	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><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%">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 this 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. </span></div>No customer accounted for more than 10% of revenue for the three and nine months ended September 30, 2021. No customer accounted for more than 10% of revenue for the three months ended September 30, 2020. One customer accounted for 11% of revenue for the nine months ended September 30, 2020. As of September 30, 2021, we had one customer that accounted for more than 10% of the total accounts receivable balance. As of December 31, 2020, we had a different customer that accounted for more than 10% of the total accounts receivable balance.
CY2020Q4	us-gaap	Contract With Customer Asset Net ContractWithCustomerAssetNet	387000	USD
CY2020Q3	us-gaap	Revenue From Contract With Customer Including Assessed Tax RevenueFromContractWithCustomerIncludingAssessedTax	70638000	USD
	us-gaap	Revenue From Contract With Customer Including Assessed Tax RevenueFromContractWithCustomerIncludingAssessedTax	256613000	USD
	us-gaap	Revenue From Contract With Customer Including Assessed Tax RevenueFromContractWithCustomerIncludingAssessedTax	208225000	USD
CY2021Q3	fsly	Enterprise Customer Threshold EnterpriseCustomerThreshold	100000	USD
CY2021Q3	us-gaap	Revenue From Contract With Customer Including Assessed Tax RevenueFromContractWithCustomerIncludingAssessedTax	86735000	USD
CY2020Q3	us-gaap	Revenue From Contract With Customer Including Assessed Tax RevenueFromContractWithCustomerIncludingAssessedTax	70638000	USD
	us-gaap	Revenue From Contract With Customer Including Assessed Tax RevenueFromContractWithCustomerIncludingAssessedTax	256613000	USD
	us-gaap	Revenue From Contract With Customer Including Assessed Tax RevenueFromContractWithCustomerIncludingAssessedTax	208225000	USD
	us-gaap	Revenue Performance Obligation Description Of Payment Terms RevenuePerformanceObligationDescriptionOfPaymentTerms	Payment terms on invoiced amounts are at an average of 40 days.
CY2021Q3	us-gaap	Contract With Customer Asset Net ContractWithCustomerAssetNet	181000	USD
CY2021Q3	us-gaap	Contract With Customer Liability ContractWithCustomerLiability	24817000	USD
CY2020Q4	us-gaap	Contract With Customer Liability ContractWithCustomerLiability	18020000	USD
CY2021Q3	us-gaap	Contract With Customer Liability Revenue Recognized ContractWithCustomerLiabilityRevenueRecognized	8815000	USD
CY2020Q3	us-gaap	Contract With Customer Liability Revenue Recognized ContractWithCustomerLiabilityRevenueRecognized	37000	USD
	us-gaap	Contract With Customer Liability Revenue Recognized ContractWithCustomerLiabilityRevenueRecognized	13942000	USD
	us-gaap	Contract With Customer Liability Revenue Recognized ContractWithCustomerLiabilityRevenueRecognized	310000	USD
CY2021Q3	us-gaap	Revenue Remaining Performance Obligation RevenueRemainingPerformanceObligation	147600000	USD
CY2021Q3	us-gaap	Revenue Remaining Performance Obligation Percentage RevenueRemainingPerformanceObligationPercentage	0.84
CY2021Q3	us-gaap	Revenue Remaining Performance Obligation Expected Timing Of Satisfaction Period1 RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1	P12M
CY2021Q3	us-gaap	Capitalized Contract Cost Amortization Period CapitalizedContractCostAmortizationPeriod	P5Y
CY2021Q3	us-gaap	Capitalized Contract Cost Net Noncurrent CapitalizedContractCostNetNoncurrent	23067000	USD
CY2020Q4	us-gaap	Capitalized Contract Cost Net Noncurrent CapitalizedContractCostNetNoncurrent	19332000	USD
CY2021Q3	us-gaap	Capitalized Contract Cost Amortization CapitalizedContractCostAmortization	1600000	USD
CY2020Q3	us-gaap	Capitalized Contract Cost Amortization CapitalizedContractCostAmortization	900000	USD
	us-gaap	Capitalized Contract Cost Amortization CapitalizedContractCostAmortization	4600000	USD
CY2021Q3	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	282131000	USD
CY2020Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	62900000	USD
CY2021Q3	us-gaap	Available For Sale Securities Debt Securities Current AvailableForSaleSecuritiesDebtSecuritiesCurrent	361290000	USD
CY2020Q4	us-gaap	Available For Sale Securities Debt Securities Current AvailableForSaleSecuritiesDebtSecuritiesCurrent	131283000	USD
CY2021Q3	us-gaap	Available For Sale Securities Debt Securities Noncurrent AvailableForSaleSecuritiesDebtSecuritiesNoncurrent	429489000	USD
CY2020Q4	us-gaap	Available For Sale Securities Debt Securities Noncurrent AvailableForSaleSecuritiesDebtSecuritiesNoncurrent	20448000	USD
CY2021Q3	us-gaap	Available For Sale Securities Debt Securities AvailableForSaleSecuritiesDebtSecurities	790779000	USD
CY2020Q4	us-gaap	Available For Sale Securities Debt Securities AvailableForSaleSecuritiesDebtSecurities	151731000	USD
CY2021Q3	fsly	Cash Cash Equivalents And Debt Securities Available For Sale CashCashEquivalentsAndDebtSecuritiesAvailableForSale	1072910000	USD
CY2020Q4	fsly	Cash Cash Equivalents And Debt Securities Available For Sale CashCashEquivalentsAndDebtSecuritiesAvailableForSale	214631000	USD
CY2021Q3	us-gaap	Available For Sale Debt Securities Amortized Cost Basis AvailableForSaleDebtSecuritiesAmortizedCostBasis	790872000	USD
CY2021Q3	us-gaap	Available For Sale Debt Securities Accumulated Gross Unrealized Gain Before Tax AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax	50000	USD
CY2021Q3	us-gaap	Available For Sale Debt Securities Accumulated Gross Unrealized Loss Before Tax AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax	143000	USD
CY2021Q3	us-gaap	Available For Sale Securities Debt Securities AvailableForSaleSecuritiesDebtSecurities	790779000	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
CY2021Q3	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
CY2021Q3	us-gaap	Cash Equivalents At Carrying Value CashEquivalentsAtCarryingValue	133480000	USD
CY2021Q3	us-gaap	Cash Equivalents At Carrying Value CashEquivalentsAtCarryingValue	133480000	USD
CY2021Q3	us-gaap	Available For Sale Securities Debt Securities AvailableForSaleSecuritiesDebtSecurities	790779000	USD
CY2021Q3	us-gaap	Restricted Cash And Cash Equivalents RestrictedCashAndCashEquivalents	893000	USD
CY2021Q3	us-gaap	Assets Fair Value Disclosure AssetsFairValueDisclosure	925152000	USD
CY2021Q3	us-gaap	Assets Fair Value Disclosure AssetsFairValueDisclosure	925152000	USD
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
CY2020	us-gaap	Business Acquisitions Pro Forma Revenue BusinessAcquisitionsProFormaRevenue	313665000	USD
CY2020	us-gaap	Business Acquisitions Pro Forma Net Income Loss BusinessAcquisitionsProFormaNetIncomeLoss	-159248000	USD
CY2020Q4	us-gaap	Finance Lease Right Of Use Asset Before Accumulated Amortization FinanceLeaseRightOfUseAssetBeforeAccumulatedAmortization	36200000	USD
CY2021Q3	us-gaap	Property Plant And Equipment Gross PropertyPlantAndEquipmentGross	228036000	USD
CY2020Q4	us-gaap	Property Plant And Equipment Gross PropertyPlantAndEquipmentGross	157632000	USD
CY2021Q3	us-gaap	Accumulated Depreciation Depletion And Amortization Property Plant And Equipment AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment	80307000	USD
CY2020Q4	us-gaap	Accumulated Depreciation Depletion And Amortization Property Plant And Equipment AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment	61653000	USD
CY2021Q3	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	147729000	USD
CY2020Q4	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	95979000	USD
CY2021Q3	us-gaap	Depreciation Depreciation	7400000	USD
CY2020Q3	us-gaap	Depreciation Depreciation	4900000	USD
	us-gaap	Depreciation Depreciation	20700000	USD
	us-gaap	Depreciation Depreciation	14300000	USD
CY2021Q3	us-gaap	Capitalized Computer Software Additions CapitalizedComputerSoftwareAdditions	5100000	USD
CY2021Q1	fsly	Capitalized Computer Software Amount Incorrectly Expensed Prior To Adjustment CapitalizedComputerSoftwareAmountIncorrectlyExpensedPriorToAdjustment	2400000	USD
CY2021Q2	fsly	Capitalized Computer Software Amount Incorrectly Expensed Prior To Adjustment CapitalizedComputerSoftwareAmountIncorrectlyExpensedPriorToAdjustment	2700000	USD
CY2021Q3	us-gaap	Finance Lease Right Of Use Asset Before Accumulated Amortization FinanceLeaseRightOfUseAssetBeforeAccumulatedAmortization	56800000	USD
CY2021Q3	us-gaap	Finance Lease Right Of Use Asset Accumulated Amortization FinanceLeaseRightOfUseAssetAccumulatedAmortization	13000000	USD
CY2020Q4	us-gaap	Finance Lease Right Of Use Asset Accumulated Amortization FinanceLeaseRightOfUseAssetAccumulatedAmortization	6700000	USD
CY2021Q3	us-gaap	Capitalized Contract Cost Net Noncurrent CapitalizedContractCostNetNoncurrent	23067000	USD
CY2020Q4	us-gaap	Capitalized Contract Cost Net Noncurrent CapitalizedContractCostNetNoncurrent	19332000	USD
CY2021Q3	us-gaap	Restricted Cash Noncurrent RestrictedCashNoncurrent	893000	USD
CY2020Q4	us-gaap	Restricted Cash Noncurrent RestrictedCashNoncurrent	893000	USD
CY2021Q3	us-gaap	Other Assets Miscellaneous Noncurrent OtherAssetsMiscellaneousNoncurrent	4182000	USD
CY2020Q4	us-gaap	Other Assets Miscellaneous Noncurrent OtherAssetsMiscellaneousNoncurrent	4692000	USD
CY2021Q3	us-gaap	Other Assets Noncurrent OtherAssetsNoncurrent	28142000	USD
CY2020Q4	us-gaap	Other Assets Noncurrent OtherAssetsNoncurrent	24917000	USD
CY2021Q3	us-gaap	Employee Related Liabilities Current EmployeeRelatedLiabilitiesCurrent	14812000	USD
CY2020Q4	us-gaap	Employee Related Liabilities Current EmployeeRelatedLiabilitiesCurrent	17840000	USD
CY2021Q3	us-gaap	Sales And Excise Tax Payable Current SalesAndExciseTaxPayableCurrent	7486000	USD
CY2020Q4	us-gaap	Sales And Excise Tax Payable Current SalesAndExciseTaxPayableCurrent	6274000	USD
CY2021Q3	fsly	Accrued Acquisition Related Costs AccruedAcquisitionRelatedCosts	0	USD
CY2020Q4	fsly	Accrued Acquisition Related Costs AccruedAcquisitionRelatedCosts	3644000	USD
CY2021Q3	fsly	Accrued Colocation And Bandwidth Costs AccruedColocationAndBandwidthCosts	7231000	USD
CY2020Q4	fsly	Accrued Colocation And Bandwidth Costs AccruedColocationAndBandwidthCosts	2208000	USD
CY2021Q3	us-gaap	Other Accrued Liabilities Current OtherAccruedLiabilitiesCurrent	6534000	USD
CY2020Q4	us-gaap	Other Accrued Liabilities Current OtherAccruedLiabilitiesCurrent	4368000	USD
CY2021Q3	us-gaap	Accrued Liabilities Current AccruedLiabilitiesCurrent	36063000	USD
CY2020Q4	us-gaap	Accrued Liabilities Current AccruedLiabilitiesCurrent	34334000	USD
CY2021Q3	us-gaap	Contract With Customer Liability Current ContractWithCustomerLiabilityCurrent	21631000	USD
CY2020Q4	us-gaap	Contract With Customer Liability Current ContractWithCustomerLiabilityCurrent	15916000	USD
CY2021Q3	fsly	Accrued Computer And Networking Equipment AccruedComputerAndNetworkingEquipment	2274000	USD
CY2020Q4	fsly	Accrued Computer And Networking Equipment AccruedComputerAndNetworkingEquipment	3126000	USD
CY2021Q3	fsly	Liability For Early Exercised Stock Options Current LiabilityForEarlyExercisedStockOptionsCurrent	213000	USD
CY2020Q4	fsly	Liability For Early Exercised Stock Options Current LiabilityForEarlyExercisedStockOptionsCurrent	255000	USD
CY2021Q3	us-gaap	Other Sundry Liabilities Current OtherSundryLiabilitiesCurrent	640000	USD
CY2020Q4	us-gaap	Other Sundry Liabilities Current OtherSundryLiabilitiesCurrent	380000	USD
CY2021Q3	us-gaap	Other Liabilities Current OtherLiabilitiesCurrent	24758000	USD
CY2020Q4	us-gaap	Other Liabilities Current OtherLiabilitiesCurrent	19677000	USD
CY2021Q3	us-gaap	Contract With Customer Liability Noncurrent ContractWithCustomerLiabilityNoncurrent	3186000	USD
CY2020Q4	us-gaap	Contract With Customer Liability Noncurrent ContractWithCustomerLiabilityNoncurrent	2104000	USD
CY2021Q3	fsly	Accrued Payroll Taxes Noncurrent Cares Act AccruedPayrollTaxesNoncurrentCARESAct	1676000	USD
CY2020Q4	fsly	Accrued Payroll Taxes Noncurrent Cares Act AccruedPayrollTaxesNoncurrentCARESAct	1676000	USD
CY2021Q3	us-gaap	Other Sundry Liabilities Noncurrent OtherSundryLiabilitiesNoncurrent	194000	USD
CY2020Q4	us-gaap	Other Sundry Liabilities Noncurrent OtherSundryLiabilitiesNoncurrent	620000	USD
CY2021Q3	us-gaap	Other Liabilities Noncurrent OtherLiabilitiesNoncurrent	5056000	USD
CY2020Q4	us-gaap	Other Liabilities Noncurrent OtherLiabilitiesNoncurrent	4400000	USD
	fsly	Subleases Remaining Lease Terms SubleasesRemainingLeaseTerms	P3Y
CY2021Q3	us-gaap	Sublease Income SubleaseIncome	200000	USD
CY2020Q3	us-gaap	Sublease Income SubleaseIncome	300000	USD
	us-gaap	Sublease Income SubleaseIncome	700000	USD
	us-gaap	Sublease Income SubleaseIncome	900000	USD
CY2021Q3	us-gaap	Operating Lease Cost OperatingLeaseCost	7018000	USD
CY2020Q3	us-gaap	Operating Lease Cost OperatingLeaseCost	5578000	USD
	us-gaap	Operating Lease Cost OperatingLeaseCost	19741000	USD
	us-gaap	Operating Lease Cost OperatingLeaseCost	15670000	USD
CY2021Q3	us-gaap	Variable Lease Cost VariableLeaseCost	1806000	USD
CY2020Q3	us-gaap	Variable Lease Cost VariableLeaseCost	1234000	USD
	us-gaap	Variable Lease Cost VariableLeaseCost	4624000	USD
	us-gaap	Variable Lease Cost VariableLeaseCost	2590000	USD
CY2021Q3	fsly	Operating Variable And Short Term Lease Costs OperatingVariableAndShortTermLeaseCosts	8824000	USD
CY2020Q3	fsly	Operating Variable And Short Term Lease Costs OperatingVariableAndShortTermLeaseCosts	6812000	USD
	fsly	Operating Variable And Short Term Lease Costs OperatingVariableAndShortTermLeaseCosts	24365000	USD
	fsly	Operating Variable And Short Term Lease Costs OperatingVariableAndShortTermLeaseCosts	18260000	USD
CY2021Q3	us-gaap	Finance Lease Right Of Use Asset Amortization FinanceLeaseRightOfUseAssetAmortization	4124000	USD
CY2020Q3	us-gaap	Finance Lease Right Of Use Asset Amortization FinanceLeaseRightOfUseAssetAmortization	419000	USD
	us-gaap	Finance Lease Right Of Use Asset Amortization FinanceLeaseRightOfUseAssetAmortization	6608000	USD
	us-gaap	Finance Lease Right Of Use Asset Amortization FinanceLeaseRightOfUseAssetAmortization	1827000	USD
CY2021Q3	us-gaap	Finance Lease Interest Expense FinanceLeaseInterestExpense	524000	USD
CY2020Q3	us-gaap	Finance Lease Interest Expense FinanceLeaseInterestExpense	186000	USD
	us-gaap	Finance Lease Interest Expense FinanceLeaseInterestExpense	1259000	USD
	us-gaap	Finance Lease Interest Expense FinanceLeaseInterestExpense	454000	USD
CY2021Q3	fsly	Finance Lease Cost FinanceLeaseCost	4648000	USD
CY2020Q3	fsly	Finance Lease Cost FinanceLeaseCost	605000	USD
	fsly	Finance Lease Cost FinanceLeaseCost	7867000	USD
	fsly	Finance Lease Cost FinanceLeaseCost	2281000	USD
CY2021Q3	us-gaap	Operating Lease Payments OperatingLeasePayments	6879000	USD
CY2020Q3	us-gaap	Operating Lease Payments OperatingLeasePayments	4439000	USD
	us-gaap	Operating Lease Payments OperatingLeasePayments	19735000	USD
	us-gaap	Operating Lease Payments OperatingLeasePayments	12852000	USD
CY2021Q3	us-gaap	Finance Lease Interest Payment On Liability FinanceLeaseInterestPaymentOnLiability	524000	USD
CY2020Q3	us-gaap	Finance Lease Interest Payment On Liability FinanceLeaseInterestPaymentOnLiability	186000	USD
	us-gaap	Finance Lease Interest Payment On Liability FinanceLeaseInterestPaymentOnLiability	1259000	USD
	us-gaap	Finance Lease Interest Payment On Liability FinanceLeaseInterestPaymentOnLiability	454000	USD
CY2021Q3	us-gaap	Finance Lease Principal Payments FinanceLeasePrincipalPayments	3985000	USD
CY2020Q3	us-gaap	Finance Lease Principal Payments FinanceLeasePrincipalPayments	1001000	USD
	us-gaap	Finance Lease Principal Payments FinanceLeasePrincipalPayments	10564000	USD
	us-gaap	Finance Lease Principal Payments FinanceLeasePrincipalPayments	3901000	USD
CY2021Q3	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	12264000	USD
CY2020Q3	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	4817000	USD
	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	25745000	USD
	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	15095000	USD
CY2021Q3	us-gaap	Right Of Use Asset Obtained In Exchange For Finance Lease Liability RightOfUseAssetObtainedInExchangeForFinanceLeaseLiability	12861000	USD
CY2020Q3	us-gaap	Right Of Use Asset Obtained In Exchange For Finance Lease Liability RightOfUseAssetObtainedInExchangeForFinanceLeaseLiability	3510000	USD
	us-gaap	Right Of Use Asset Obtained In Exchange For Finance Lease Liability RightOfUseAssetObtainedInExchangeForFinanceLeaseLiability	28399000	USD
	us-gaap	Right Of Use Asset Obtained In Exchange For Finance Lease Liability RightOfUseAssetObtainedInExchangeForFinanceLeaseLiability	11352000	USD
CY2021Q3	us-gaap	Operating Lease Weighted Average Remaining Lease Term1 OperatingLeaseWeightedAverageRemainingLeaseTerm1	P4Y5M8D
CY2020Q4	us-gaap	Operating Lease Weighted Average Remaining Lease Term1 OperatingLeaseWeightedAverageRemainingLeaseTerm1	P4Y5M8D
CY2021Q3	us-gaap	Finance Lease Weighted Average Remaining Lease Term1 FinanceLeaseWeightedAverageRemainingLeaseTerm1	P2Y3M3D
CY2020Q4	us-gaap	Finance Lease Weighted Average Remaining Lease Term1 FinanceLeaseWeightedAverageRemainingLeaseTerm1	P2Y6M3D
CY2021Q3	us-gaap	Operating Lease Weighted Average Discount Rate Percent OperatingLeaseWeightedAverageDiscountRatePercent	0.0529
CY2020Q4	us-gaap	Operating Lease Weighted Average Discount Rate Percent OperatingLeaseWeightedAverageDiscountRatePercent	0.0568
CY2021Q3	us-gaap	Finance Lease Weighted Average Discount Rate Percent FinanceLeaseWeightedAverageDiscountRatePercent	0.0492
CY2020Q4	us-gaap	Finance Lease Weighted Average Discount Rate Percent FinanceLeaseWeightedAverageDiscountRatePercent	0.0512
CY2021Q3	fsly	Lessee Operating Lease Lease Not Yet Commenced Commitment Amount LesseeOperatingLeaseLeaseNotYetCommencedCommitmentAmount	7000000	USD
CY2021Q3	us-gaap	Lessee Operating Lease Liability Payments Remainder Of Fiscal Year LesseeOperatingLeaseLiabilityPaymentsRemainderOfFiscalYear	7108000	USD
CY2021Q3	us-gaap	Finance Lease Liability Payments Remainder Of Fiscal Year FinanceLeaseLiabilityPaymentsRemainderOfFiscalYear	5268000	USD
CY2021Q3	us-gaap	Lessee Operating Lease Liability Payments Due Next Twelve Months LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths	24241000	USD
CY2021Q3	us-gaap	Finance Lease Liability Payments Due Next Twelve Months FinanceLeaseLiabilityPaymentsDueNextTwelveMonths	19414000	USD
CY2021Q3	us-gaap	Lessee Operating Lease Liability Payments Due Year Two LesseeOperatingLeaseLiabilityPaymentsDueYearTwo	17710000	USD
CY2021Q3	us-gaap	Finance Lease Liability Payments Due Year Two FinanceLeaseLiabilityPaymentsDueYearTwo	15930000	USD
CY2021Q3	us-gaap	Lessee Operating Lease Liability Payments Due Year Three LesseeOperatingLeaseLiabilityPaymentsDueYearThree	13337000	USD
CY2021Q3	us-gaap	Finance Lease Liability Payments Due Year Three FinanceLeaseLiabilityPaymentsDueYearThree	4788000	USD
CY2021Q3	us-gaap	Lessee Operating Lease Liability Payments Due Year Four LesseeOperatingLeaseLiabilityPaymentsDueYearFour	12395000	USD
CY2021Q3	us-gaap	Finance Lease Liability Payments Due Year Four FinanceLeaseLiabilityPaymentsDueYearFour	0	USD
CY2021Q3	fsly	Lessee Operating Lease Liability To Be Paid After Year Four LesseeOperatingLeaseLiabilityToBePaidAfterYearFour	17208000	USD
CY2021Q3	fsly	Finance Lease Liability To Be Paid After Year Four FinanceLeaseLiabilityToBePaidAfterYearFour	0	USD
CY2021Q3	us-gaap	Lessee Operating Lease Liability Payments Due LesseeOperatingLeaseLiabilityPaymentsDue	91999000	USD
CY2021Q3	us-gaap	Finance Lease Liability Payments Due FinanceLeaseLiabilityPaymentsDue	45400000	USD
CY2021Q3	us-gaap	Lessee Operating Lease Liability Undiscounted Excess Amount LesseeOperatingLeaseLiabilityUndiscountedExcessAmount	9943000	USD
CY2021Q3	us-gaap	Finance Lease Liability Undiscounted Excess Amount FinanceLeaseLiabilityUndiscountedExcessAmount	2062000	USD
CY2021Q3	us-gaap	Operating Lease Liability OperatingLeaseLiability	82056000	USD
CY2021Q3	us-gaap	Finance Lease Liability FinanceLeaseLiability	43338000	USD
CY2020Q4	us-gaap	Goodwill Goodwill	635590000	USD
	us-gaap	Goodwill Foreign Currency Translation Gain Loss GoodwillForeignCurrencyTranslationGainLoss	45000	USD
CY2021Q3	us-gaap	Goodwill Goodwill	635635000	USD
CY2021Q3	us-gaap	Intangible Assets Gross Excluding Goodwill IntangibleAssetsGrossExcludingGoodwill	129491000	USD
CY2021Q3	us-gaap	Finite Lived Intangible Assets Accumulated Amortization FiniteLivedIntangibleAssetsAccumulatedAmortization	21586000	USD
CY2021Q3	us-gaap	Intangible Assets Net Excluding Goodwill IntangibleAssetsNetExcludingGoodwill	107905000	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
	us-gaap	Payments To Acquire Intangible Assets PaymentsToAcquireIntangibleAssets	2100000	USD
	us-gaap	Payments To Acquire Intangible Assets PaymentsToAcquireIntangibleAssets	1800000	USD
CY2021Q3	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	5300000	USD
	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	15900000	USD
CY2020Q3	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	100000	USD
	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	100000	USD
CY2021Q3	us-gaap	Finite Lived Intangible Assets Amortization Expense Remainder Of Fiscal Year FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear	5313000	USD
CY2021Q3	us-gaap	Finite Lived Intangible Assets Amortization Expense Next Twelve Months FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths	20974000	USD
CY2021Q3	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Two FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo	19874000	USD
CY2021Q3	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Three FiniteLivedIntangibleAssetsAmortizationExpenseYearThree	19040000	USD
CY2021Q3	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Four FiniteLivedIntangibleAssetsAmortizationExpenseYearFour	16561000	USD
CY2021Q3	fsly	Finite Lived Intangible Assets Amortization Expense After Year Four FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFour	25771000	USD
CY2021Q3	us-gaap	Finite Lived Intangible Assets Net FiniteLivedIntangibleAssetsNet	107533000	USD
CY2020Q4	us-gaap	Line Of Credit LineOfCredit	20300000	USD
CY2020Q4	fsly	Cash Collateral For Line Of Credit CashCollateralForLineOfCredit	70100000	USD
CY2021Q3	us-gaap	Interest Expense Debt InterestExpenseDebt	1000000	USD
	us-gaap	Interest Expense Debt InterestExpenseDebt	2400000	USD
CY2020Q3	us-gaap	Interest Expense Debt InterestExpenseDebt	400000	USD
	us-gaap	Interest Expense Debt InterestExpenseDebt	1100000	USD
CY2021Q3	us-gaap	Purchase Obligation Future Minimum Payments Remainder Of Fiscal Year PurchaseObligationFutureMinimumPaymentsRemainderOfFiscalYear	17849000	USD
CY2021Q3	us-gaap	Purchase Obligation Due In Next Twelve Months PurchaseObligationDueInNextTwelveMonths	42361000	USD
CY2021Q3	us-gaap	Purchase Obligation Due In Second Year PurchaseObligationDueInSecondYear	18316000	USD
CY2021Q3	us-gaap	Purchase Obligation Due In Third Year PurchaseObligationDueInThirdYear	3060000	USD
CY2021Q3	us-gaap	Purchase Obligation Due In Fourth Year PurchaseObligationDueInFourthYear	160000	USD
CY2021Q3	fsly	Purchase Obligation Due After Fourth Year PurchaseObligationDueAfterFourthYear	46000	USD
CY2021Q3	us-gaap	Purchase Obligation PurchaseObligation	81792000	USD
CY2021Q3	us-gaap	Sales And Excise Tax Payable Current And Noncurrent SalesAndExciseTaxPayableCurrentAndNoncurrent	7500000	USD
CY2020Q4	us-gaap	Sales And Excise Tax Payable Current And Noncurrent SalesAndExciseTaxPayableCurrentAndNoncurrent	6300000	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	shares
CY2019Q2	us-gaap	Preferred Stock Par Or Stated Value Per Share PreferredStockParOrStatedValuePerShare	0.00002
CY2021Q3	us-gaap	Preferred Stock Shares Issued PreferredStockSharesIssued	0	shares
CY2020Q4	us-gaap	Preferred Stock Shares Outstanding PreferredStockSharesOutstanding	0	shares
CY2020Q4	us-gaap	Preferred Stock Shares Issued PreferredStockSharesIssued	0	shares
CY2021Q3	us-gaap	Preferred Stock Shares Outstanding PreferredStockSharesOutstanding	0	shares
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
	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Gross ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross	0	shares
	us-gaap	Share Based Compensation Arrangements By Share Based Payment Award Options Grants In Period Weighted Average Exercise Price ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice	0
	us-gaap	Stock Issued During Period Shares Stock Options Exercised StockIssuedDuringPeriodSharesStockOptionsExercised	1527000	shares
	us-gaap	Share Based Compensation Arrangements By Share Based Payment Award Options Exercises In Period Weighted Average Exercise Price ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice	5.96
	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Forfeitures And Expirations In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod	261000	shares
	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Forfeitures And Expirations In Period Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriodWeightedAverageExercisePrice	11.00
CY2021Q3	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Number ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber	5175000	shares
CY2021Q3	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice	5.27
	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Outstanding Weighted Average Remaining Contractual Term2 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2	P5Y2M12D
CY2021Q3	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue	182027000	USD
CY2021Q3	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Vested And Expected To Vest Exercisable Number ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableNumber	3912000	shares
CY2021Q3	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Vested And Expected To Vest Exercisable Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageExercisePrice	3.97
	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Vested And Expected To Vest Exercisable Weighted Average Remaining Contractual Term1 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageRemainingContractualTerm1	P4Y7M6D
CY2021Q3	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Vested And Expected To Vest Exercisable Aggregate Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableAggregateIntrinsicValue	142675000	USD
CY2021Q3	fsly	Share Based Compensation Arrangement By Share Based Payment Award Options Unvested Exercisable Number ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsUnvestedExercisableNumber	173000	shares
CY2021Q3	fsly	Share Based Compensation Arrangement By Share Based Payment Award Options Unvested Exercisable Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsUnvestedExercisableWeightedAverageExercisePrice	6.65
	fsly	Share Based Compensation Arrangement By Share Based Payment Award Options Unvested Exercisable Weighted Average Remaining Contractual Term ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsUnvestedExercisableWeightedAverageRemainingContractualTerm	P7Y1M6D
CY2021Q3	fsly	Share Based Compensation Arrangement By Share Based Payment Award Options Unvested Exercisable Aggregate Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsUnvestedExercisableAggregateIntrinsicValue	5841000	USD
	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Exercises In Period Total Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue	52600000	USD
	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Exercises In Period Total Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue	157900000	USD
	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Vested In Period Fair Value1 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1	8300000	USD
	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Vested In Period Fair Value1 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1	6500000	USD
	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Gross ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross	0	shares
CY2020Q3	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Gross ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross	0	shares
	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Gross ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross	0	shares
CY2021Q3	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Gross ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross	0	shares
CY2021Q3	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Accelerated Compensation Cost ShareBasedCompensationArrangementByShareBasedPaymentAwardAcceleratedCompensationCost	2400000	USD
	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Accelerated Compensation Cost ShareBasedCompensationArrangementByShareBasedPaymentAwardAcceleratedCompensationCost	3700000	USD
CY2021Q3	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Plan Modification Incremental Compensation Cost ShareBasedCompensationArrangementByShareBasedPaymentAwardPlanModificationIncrementalCompensationCost	2100000	USD
	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Plan Modification Incremental Compensation Cost ShareBasedCompensationArrangementByShareBasedPaymentAwardPlanModificationIncrementalCompensationCost	3300000	USD
	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Accelerated Compensation Cost ShareBasedCompensationArrangementByShareBasedPaymentAwardAcceleratedCompensationCost	400000	USD
CY2020Q3	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Accelerated Compensation Cost ShareBasedCompensationArrangementByShareBasedPaymentAwardAcceleratedCompensationCost	400000	USD
	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Plan Modification Incremental Compensation Cost ShareBasedCompensationArrangementByShareBasedPaymentAwardPlanModificationIncrementalCompensationCost	300000	USD
CY2020Q3	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Plan Modification Incremental Compensation Cost ShareBasedCompensationArrangementByShareBasedPaymentAwardPlanModificationIncrementalCompensationCost	300000	USD
CY2021Q3	us-gaap	Employee Service Share Based Compensation Nonvested Awards Total Compensation Cost Not Yet Recognized Stock Options EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions	14500000	USD
CY2021Q3	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Nonvested Number Of Shares SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfShares	47882	shares
CY2020Q4	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Nonvested Number Of Shares SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfShares	90977	shares
CY2021Q3	fsly	Amount Withheld In Contributions For Employee Stock Purchase Plan AmountWithheldInContributionsForEmployeeStockPurchasePlan	3500000	USD
	fsly	Amount Withheld In Contributions For Employee Stock Purchase Plan AmountWithheldInContributionsForEmployeeStockPurchasePlan	6000000	USD
CY2020Q3	fsly	Amount Withheld In Contributions For Employee Stock Purchase Plan AmountWithheldInContributionsForEmployeeStockPurchasePlan	2000000	USD
	fsly	Amount Withheld In Contributions For Employee Stock Purchase Plan AmountWithheldInContributionsForEmployeeStockPurchasePlan	6100000	USD
	us-gaap	Stock Repurchased During Period Shares StockRepurchasedDuringPeriodShares	200000	shares
	us-gaap	Stock Repurchased During Period Shares StockRepurchasedDuringPeriodShares	200000	shares
CY2021Q3	us-gaap	Allocated Share Based Compensation Expense AllocatedShareBasedCompensationExpense	36636000	USD
CY2020Q3	us-gaap	Allocated Share Based Compensation Expense AllocatedShareBasedCompensationExpense	12142000	USD
	us-gaap	Allocated Share Based Compensation Expense AllocatedShareBasedCompensationExpense	100900000	USD
	us-gaap	Allocated Share Based Compensation Expense AllocatedShareBasedCompensationExpense	34752000	USD
CY2021Q3	us-gaap	Employee Service Share Based Compensation Allocation Of Recognized Period Costs Capitalized Amount EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount	2600000	USD
	us-gaap	Employee Service Share Based Compensation Allocation Of Recognized Period Costs Capitalized Amount EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount	3400000	USD
CY2020Q3	us-gaap	Employee Service Share Based Compensation Allocation Of Recognized Period Costs Capitalized Amount EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount	600000	USD
	us-gaap	Employee Service Share Based Compensation Allocation Of Recognized Period Costs Capitalized Amount EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount	1200000	USD
	us-gaap	Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	19550000	shares
	us-gaap	Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	11928000	shares
CY2021Q3	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	30000.00	USD
CY2020Q3	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	300000	USD
	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	40000.00	USD
	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	1100000	USD
	us-gaap	Number Of Reportable Segments NumberOfReportableSegments	1	segment
CY2021Q3	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	147729000	USD
CY2020Q4	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	95979000	USD

Files In Submission

Name	View Source	Status
0001517413-21-000195-index-headers.html	Edgar Link	pending
0001517413-21-000195-index.html	Edgar Link	pending
0001517413-21-000195.txt	Edgar Link	pending
0001517413-21-000195-xbrl.zip	Edgar Link	pending
FilingSummary.xml	Edgar Link	unprocessable
Financial_Report.xlsx	Edgar Link	pending
fsly-20210930.htm	Edgar Link	pending
fsly-20210930.xsd	Edgar Link	pending
fsly-20210930_cal.xml	Edgar Link	unprocessable
fsly-20210930_def.xml	Edgar Link	unprocessable
fsly-20210930_htm.xml	Edgar Link	completed
fsly-20210930_lab.xml	Edgar Link	unprocessable
fsly-20210930_pre.xml	Edgar Link	unprocessable
fsly-93021x10qexhibit311.htm	Edgar Link	pending
fsly-93021x10qexhibit312.htm	Edgar Link	pending
fsly-93021x10qexhibit321.htm	Edgar Link	pending
fsly-93021x10qexhibit322.htm	Edgar Link	pending
MetaLinks.json	Edgar Link	pending
R1.htm	Edgar Link	pending
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report.css	Edgar Link	pending
Show.js	Edgar Link	pending

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$FSLY
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2021 Q4 Form 10-Q Financial Statement

#000151741321000195 Filed on November 08, 2021

Income Statement

Balance Sheet

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Facts In Submission

Files In Submission

$FSLY Fastly Inc Stock $fsly

2021 Q4 Form 10-Q Financial Statement

#000151741321000195 Filed on November 08, 2021

Income Statement

Balance Sheet

Cashflow Statement

Facts In Submission

Files In Submission

$FSLY
Fastly Inc Stock $fsly