Income Taxes (Tables)

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Schedule of Effective Tax Rate Reconciliation

The Company's effective tax rate differs from the federal statutory rate as follows:

	Year Ended December 31,
	2019		2018		2017
Taxes at the U.S. statutory tax rate	21.0	%	21.0	%	34.0	%
Effect of Tax Act	—		—		(26.6)
Change in valuation allowance	(24.4)		(20.7)		(7.3)
Research tax credits	3.5		10.2		1.0
Stock-based compensation	0.1		(0.7)		(1.0)
Nondeductible acquisition-related costs	—		(9.5)		—
Other	(0.1)		(0.3)		(0.1)
Total provision for income taxes	0.1	%	—	%	—	%

Schedule of Deferred Tax Assets and Liabilities

The components of the Company’s net deferred tax assets are as follows (in thousands):

	December 31,
	2019		2018
Deferred tax assets:
Net operating loss carryforwards	$	56,612	$	35,023
Tax credit carryforwards	19,133		9,565
Contract liabilities	13,516		—
Operating lease liability	15,686		—
Stock-based compensation	9,513		3,305
Accruals and other	11,815		17,181
Gross deferred tax assets	126,275		65,074
Valuation allowance	(112,713)		(60,915)
Net deferred tax assets	13,562		4,159
Deferred tax liabilities:
Property and equipment	(6,225)		(4,159)
Operating lease right-of-use asset	(7,337)		—
Net deferred tax assets	$	—	$	—

Schedule of Reconciliation of Unrecognized Tax Benefits

A reconciliation of the beginning and ending amounts of unrecognized tax benefits is as follows (in thousands):

	December 31,
	2019		2018		2017
Unrecognized tax benefits at January 1	$	2,642	$	1,146	$	531
Additions for tax positions taken in a prior year	107		—		—
Additions for tax positions taken in the current year	2,595		1,506		640
Reductions for tax positions taken in the prior year	(45)		(10)		(25)
Unrecognized tax benefits at December 31	$	5,299	$	2,642	$	1,146