Income Taxes (Tables)

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Schedule of Income Tax Rate Reconciliation Components

The components of our provision for income taxes are as follows:

	Year Ended December 31,
	2018		2017		2016
Tax at federal statutory rate	21.0	%	35.0	%	35.0	%
State, net of federal benefit	4.0		3.0		2.8
Permanent items	0.1		(1.1)		(0.5)
Research and development ("R&D") tax credit	1.3		1.2		1.3
Federal tax rate change	—		(92.6)		—
Other	(0.1)		1.1		7.1
Change in valuation allowance	(26.3)		53.4		(45.7)
Total	—	%	—	%	—	%

Schedule of Deferred Tax Assets and Liabilities

Significant components of net deferred tax assets and liabilities were as follows:

	Year Ended December 31,
	2018		2017		2016
Deferred tax assets:
Net operating losses	$	31,120	$	27,827	$	36,626
R&D tax credits	1,916		1,368		1,093
R&D expenditures, capitalized for tax	2,549		2,146		2,682
Interest expense carryforward	638		—		—
Accruals and other	1,688		753		1,065
Depreciation and amortization	31		4		—
Other comprehensive loss	16		—		—
Total deferred tax assets	37,958		32,098		41,466
Deferred tax liabilities:
Depreciation and amortization	—		—		(4)
Other	(101)		—		—
Total deferred tax liabilities	(101)		—		(4)
Net deferred tax assets	37,857		32,098		41,462
Valuation allowance	(37,857)		(32,098)		(41,462)
	$	—	$	—	$	—