Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

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,
	2017				2016				2015
Expected income tax benefit at the federal    statutory rate		34.0		%		34.0		%		34.0		%
State taxes, net of federal benefit		0.0				0.0				(0.8	)
Change in effective tax rate		(54.1	)			0.0				(0.9	)
Non-deductible items and other		0.5				(0.7	)			(0.5	)
Federal and state credits		0.5				0.6				(0.7	)
Change in valuation allowance		19.1				(33.9	)			(31.1	)
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, 2017 and 2016 (in thousands):

	Year Ended December 31,
	2017			2016
Net operating loss carryforwards	$	61,049		$	75,036
Research and development tax credits		3,731			2,131
Reserves and accruals		1,168			1,791
Other		6,611			4,594
Total deferred tax assets		72,559			83,552
Valuation allowance		(72,559	)		(83,552	)
Net deferred tax assets	$	—		$	—

Schedule of Unrecognized Tax Benefits

At December 31, 2017 and 2016, the Company’s unrecognized tax benefits consist of the following:

	Year Ended December 31,
	2017			2016
Unrecognized tax benefit, beginning of period	$	940		$	742
Gross increases — current year tax positions		327			198
Gross increases — prior year tax positions		73			—
Gross decreases — prior year tax positions		(205	)		—
Unrecognized tax benefit, end of period	$	1,135		$	940