Income Taxes (Tables)

12 Months Ended

Dec. 31, 2016

Income Tax Disclosure [Abstract]

Loss Before Income Taxes

Loss before income taxes for the years ended December 31 consisted of the following (in thousands):

	2016			2015			2014
Domestic	$	(47,562	)	$	(46,065	)	$	(50,455	)
Foreign	589			650			417
Loss before income taxes	$	(46,973	)	$	(45,415	)	$	(50,038	)

Significant Components of our Provision for Income Taxes

Significant components of our provision for income taxes for the years ended December 31 are as follows (in thousands):

	2016		2015		2014
Current:
Domestic	$	—	$	—	$	—
Foreign	116		166		—
Total provision for income taxes	$	116	$	166	$	—

Income Tax Expense (Benefit) Differed from Amounts Computed by Applying Statutory Federal Income Tax Rate

Income tax expense (benefit) differed from the amounts computed by applying the statutory federal income tax rate of 34% to pretax loss as a result of the following for the years ended December 31 (in thousands):

	2016			2015			2014
Income tax provision at statutory rate	$	(16,010	)	$	(15,662	)	$	(17,013	)
Nondeductible items	135			401			456
Change in tax credits	(1,449		)	(792		)	(678		)
Change in valuation allowance	17,824			16,706			17,911
Foreign tax and other	(384		)	(487		)	(676		)
Total provision for income taxes	$	116		$	166		$	—

Effect of Temporary Differences and Carryforwards

The effect of temporary differences and carryforwards that give rise to deferred tax assets for the years ended December 31 were as follows (in thousands):

	2016			2015
Net operating loss carryforwards	$	70,694		$	57,158
Research and development tax credit carryforwards	4,572			3,124
Stock-based compensation	5,360			3,212
Other	7,827			7,135
Total deferred tax assets	88,453			70,629
Less: Valuation allowance	(88,453		)	(70,629		)
Net deferred tax assets	$	—		$	—

Summary of Changes in Deferred Tax Asset Valuation Allowance

The table below summarizes changes in the deferred tax asset valuation allowance for the years ended December 31 (in thousands):

	2016		2015		2014
Balance at beginning of year	$	70,629	$	53,923	$	36,012
Charged to costs and expenses	17,824		16,706		17,911
Write-offs	—		—		—
Balance at end of year	$	88,453	$	70,629	$	53,923

Total Balance of Unrecognized Gross Tax Benefits Resulting from R&D Credits Claimed

The total balance of unrecognized gross tax benefits for the years ended December 31, resulting from research and development tax credits claimed on the Company’s annual tax return was as follows (in thousands):

	2016		2015		2014
Unrecognized tax benefits at beginning of year	$	1,041	$	777	$	551
Additions (reductions) based on current year tax positions	483		264		226
Unrecognized tax benefits at end of year	$	1,524	$	1,041	$	777