Income Taxes (Tables)

12 Months Ended

Dec. 31, 2015

Income Tax Disclosure [Abstract]

Net Loss before Income Tax Based on Jurisdictions

Our net loss before income tax was subject to tax in the following jurisdictions for the following periods (in thousands):

	Year Ended December 31,
	2015			2014			2013
United States	$	(51,779	)	$	(47,482	)	$	(32,524	)
Foreign	(244		)	(185		)	(194		)
	$	(52,023	)	$	(47,667	)	$	(32,718	)

Income Tax Rate Reconciliation

Our rate reconciliation consists of the following:

	Year Ended December 31,
	2015		2014		2013
Federal statutory rate	35.0	%	35.0	%	35.0	%
State tax (net of federal benefit)	5.8	%	5.4	%	5.3	%
Research and development credits	3.0	%	3.8	%	3.9	%
Warrants/purchase rights liabilities	0.0	%	2.2	%	(1.6	)%
Foreign net operating losses	(0.2	)%	(0.4	)%	(1.2	)%
382 limited net operating losses and credits	0.0	%	0.0	%	(0.6	)%
Change in valuation allowance	(43.3	)%	(45.1	)%	(40.0	)%
Other	(0.3	)%	(0.9	)%	(0.8	)%
Effective tax rate	0.0	%	0.0	%	0.0	%

Deferred Tax Assets

Significant components of our deferred tax assets are shown below. A valuation allowance has been established as realization of such deferred tax assets has not met the more likely-than-not threshold requirement. If our judgment changes and it is determined that we will be able to realize these deferred tax assets, the tax benefits relating to any reversal of the valuation allowance on deferred tax assets will be accounted for as a reduction to income tax expense.

	December 31,
	2015			2014
	(in thousands)
Deferred tax assets:
Net operating loss carryforwards	$	53,218		$	33,517
Research and development tax credits	4,903			3,269
Stock compensation	2,000			879
Foreign net operating loss carryforwards	333			377
Other, net	1,823			1,715
Total deferred tax assets	62,277			39,757
Less valuation allowance	(62,277		)	(39,757		)
	$	—		$	—

Unrecognized Tax Benefit

The following table summarizes the activity related to our unrecognized tax benefits (in thousands):

	Year Ended December 31,
	2015		2014
Balance at beginning of year	$	938	$	407
Additions based on tax positions related to the current year	484		533
Changes for prior period tax positions	—		(2		)
Balance at end of year	$	1,422	$	938