Income Taxes (Tables)

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Schedule of Reconciliation of Differences Between Federal Income Tax Rate and Effective Tax Rate

The following reconciles the differences between income taxes computed at the federal income tax rate and the provision for income taxes:

	Year Ended December 31,
	2018				2017				2016
Expected income tax benefit at the federal    statutory rate		21.0		%		34.0		%		34.0		%
State taxes, net of federal benefit		0.0				0.0				0.0
Change in federal statutory rate		0.0				(54.1	)			0.0
Non-deductible items and other		(0.2	)			0.5				(0.7	)
Federal and state credits		0.7				0.5				0.6
Change in valuation allowance		(21.5	)			19.1				(33.9	)
Total		0.0		%		0.0		%		0.0		%

Schedule of Deferred Tax Assets

The principal components of the Company’s net deferred tax assets consisted of the following at December 31, 2018 and 2017 (in thousands):

	Year Ended December 31,
	2018			2017
Net operating loss carryforwards	$	76,753		$	61,049
Research and development tax credits		4,699			3,731
Reserves and accruals		1,444			1,168
Other		9,109			6,611
Total deferred tax assets		92,005			72,559
Valuation allowance		(92,005	)		(72,559	)
Net deferred tax assets	$	—		$	—

Schedule of Unrecognized Tax Benefits

At December 31, 2018 and 2017, the Company’s unrecognized tax benefits consist of the following:

	Year Ended December 31,
	2018		2017
Unrecognized tax benefit, beginning of period	$	1,135	$	940
Gross increases — current year tax positions		422		327
Gross increases — prior year tax positions		38		73
Gross decreases — prior year tax positions		—		(205	)
Unrecognized tax benefit, end of period	$	1,595	$	1,135