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Income Taxes (Tables)

12 Months Ended

Dec. 31, 2020

Income Taxes [Abstract]

Reconciliation of Federal Income Tax Rate

	Years ended December 31,
	2020			2019			2018
Statutory tax rate	21.0	%		21.0	%		21.0	%
State tax rate, net of federal benefit	(8.3)			4.9			3.5
Stock-based compensation	(15.2)			(0.8)			(1.6)
Tax credits	(3.6)			2.2			2.0
Other	(0.2)			0.2			(0.1)
Change in valuation allowance	6.3			(27.5)			(24.8)
Total	-	%		-	%		-	%

Reconciliation of Deferred Tax Assets and Liabilities

	December 31,
Deferred tax assets:	2020			2019
Net operating loss carryforwards	$	233,225		$	226,911
Research and development credits		49,179			45,853
Accruals and reserves		6,337			8,024
Stock-based compensation		9,717			16,219
ASC842 Operating lease liability		9,870			10,837
Total deferred tax assets		308,328			307,844
Less: Valuation allowance		(300,505)			(298,658)
Total deferred tax assets:		7,823			9,186
Fixed assets		(786)			(1,425)
ASC842 Operating lease right-of-use assets		(7,037)			(7,761)
Total deferred tax liabilities		(7,823)			(9,186)
Net deferred tax assets	$	—		$	—

Reconciliation of Unrecognized Tax Benefit Accounts

Balance as of December 31, 2017	$	18,786
Decrease in balance related to tax positions taken in prior year		—
Increase in balance related to tax positions taken during current year		1,661
Balance as of December 31, 2018	$	20,447
Decrease in balance related to tax positions taken in prior year		—
Increase in balance related to tax positions taken during current year		1,532
Balance as of December 31, 2019	$	21,979
Decrease in balance related to tax positions taken in prior year		(17,255)
Increase in balance related to tax positions taken during current year		1,230
Balance as of December 31, 2020	$	5,954

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Tabular disclosure of the components of net deferred tax asset or liability recognized in an entity's statement of financial position, including the following: the total of all deferred tax liabilities, the total of all deferred tax assets, the total valuation allowance recognized for deferred tax assets.

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Tabular disclosure of the reconciliation using percentage or dollar amounts of the reported amount of income tax expense attributable to continuing operations for the year to the amount of income tax expense that would result from applying domestic federal statutory tax rates to pretax income from continuing operations.

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Tabular disclosure of the change in unrecognized tax benefits.

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