Income Taxes - Effective Income Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Net loss before tax	$ (357,937)	$ (213,256)	$ (98,418)
Statutory combined U.S. federal and state tax rate (as a percent)	21.00%	21.00%	21.00%
Statutory federal and state taxes	$ (75,167)	$ (44,784)	$ (20,668)
State income taxes, net of federal benefit	(13,490)	0	0
Effect of change in valuation allowance	110,985	52,719	25,959
Non-deductible share-based compensation	2,724	1,810	884
Tax deductions for share-based compensation	(17,991)	(6,917)	(2,924)
Tax credits	(15,672)	(8,621)	(5,130)
Uncertain tax positions	3,857	2,143	1,283
Return to provision and other true-ups	25	(60)	375
Non-deductible officers' compensation	4,697	3,527	179
Other differences	32	183	42
Income tax benefit	$ 0	$ 0	$ 0

Effective Income Tax Rate Reconciliation, Combined Federal and State Statutory Income Tax Rate, Percent

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Effective Income Tax Rate Reconciliation, Non-Deductible Officers' Compensation, Amount

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Amount of difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying domestic federal statutory income tax rate to pretax income (loss) from continuing operation, attributable to expense for award under share-based payment arrangement. Excludes expense determined to be nondeductible upon grant or after for award under share-based payment arrangement.

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Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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The amount of income tax expense or benefit for the period computed by applying the domestic federal statutory tax rates to pretax income from continuing operations.

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Amount of reported income tax expense (benefit) in excess of (less than) expected income tax expense (benefit) computed by applying domestic federal statutory income tax rate to pretax income (loss) from continuing operation, attributable to nondeductible expense for award under share-based payment arrangement. Includes, but is not limited to, expense determined to be nondeductible upon grant or after for award under share-based payment arrangement.

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