Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Taxes

Summary of loss before income taxes

	Year Ended December 31,
	2017		2016		2015
U.S. operations	$	8,347	$	28,643	$	24,850
Foreign operations		10,551		—		—
Loss before income taxes	$	18,898		28,643		24,850

Schedule of components of the net deferred tax asset

The components of the net deferred tax asset are as follows (in thousands):

	December 31,
	2017		2016
Gross deferred tax assets:
Net operating loss carryforwards	$	35,559	$	48,654
Accrued expenses		52		55
Contributions		4		6
Deferred expenses		35		58
Stock‑based compensation		1,459		1,523
Research and development and other credits		5,536		5,258
Total gross deferred tax assets		42,645		55,554
Gross deferred tax liabilities:
Depreciation		(17)		(3)
Total gross deferred tax liabilities		(17)		(3)
Net deferred tax assets		42,628		55,551
Less: valuation allowance		(42,628)		(55,551)
Net deferred tax assets after valuation allowance	$	—	$	—

Schedule of reconciliation of income tax expense (benefit) at the statutory federal income tax rate and income taxes

	Year Ended December 31,
	2017		2016		2015
Federal income tax expense at statutory rate	34.0	%	34.0	%	34.0	%
Permanent items	(0.6)		(1.2)		(1.0)
State income tax, net of federal benefit	2.8		7.5		7.1
R&D tax credits	1.1		5.2		4.2
Change in federal statutory rate on deferreds	(85.6)		—		—
Foreign income tax effect	(19.0)		—		—
Other	(1.1)		1.6		5.0
Change in valuation allowance	68.4		(47.1)		(49.3)
Effective income tax rate	0.0	%	0.0	%	0.0	%