Income Taxes - (Tables)

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Schedule of Effective Income Tax Rate Reconciliation

The following table reconciles the federal statutory income rate to the Company's effective income tax rate:

	Year Ended December 31,
	2019		2018		2017
Statutory U.S. federal rate	21.0	%	21.0	%	34.0	%
State income taxes - net of federal benefit	6.3	%	7.0	%	5.8	%
Permanent items	(2.1	)%	(0.5	)%	(0.1	)%
Research tax credits/other	1.1	%	1.6	%	0.5	%
Change in enacted rates	—	%	—	%	(35.8	)%
Valuation allowance, net	(26.3	)%	(29.1	)%	(6.7	)%
Other	—	%	—	%	2.3	%
Effective income tax rate	—	%	—	%	—	%

Schedule of Deferred Tax Assets and Liabilities

The tax effects of temporary differences that give rise to the Company's net deferred tax assets are as follows (in thousands):

	Year Ended December 31,
	2019			2018
Deferred Tax Assets
Net operating loss carryforwards	$	71,270		$	59,126
Research and development credits	6,586			5,780
Stock-based compensations expense	2,516			1,946
Deferred rent and other expenses	812			458
Deferred revenue	4,468			4,037
Operating lease liability	102			—
Patent costs/amortization	5,111			4,881
Gross deferred tax assets	90,865			76,228
Deferred Tax Liabilities
Depreciation	$	(57	)	$	(66	)
Operating lease right-of-use asset	(82		)	—
Gross deferred tax liabilities	(139		)	(66		)
Net deferred tax assets before valuation allowance	90,726			76,162
Valuation allowance	(90,726		)	(76,162		)
Net deferred tax assets	$	—		$	—