Income Taxes (Tables)

12 Months Ended

Dec. 31, 2015

Income Tax Disclosure [Abstract]

Loss Before Income Taxes

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

	2015			2014			2013
Domestic	$	(46,065	)	$	(50,455	)	$	(28,746	)
Foreign		650			417			(535	)
Loss before income taxes	$	(45,415	)	$	(50,038	)	$	(29,281	)

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):

	2015		2014		2013
Current:
Domestic	$	—	$	—	$	—
Foreign		166		—		—
Total current provision		166		—		—
Deferred:
Domestic		—		—		—
Foreign		—		—		—
Total deferred provision		—		—		—
Total provision for income taxes	$	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):

	2015			2014			2013
Income tax provision at statutory rate	$	(15,662	)	$	(17,013	)	$	(9,955	)
Nondeductible items		401			456			(32	)
Change in tax credits		(792	)		(678	)		(893	)
Change in valuation allowance		16,706			17,911			10,965
Foreign tax and other		(487	)		(676	)		(85	)
	$	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):

	2015			2014
Net operating loss carryforwards	$	57,158		$	47,444
Research and development tax credit carryforwards		3,124			2,332
Stock-based compensation		3,212			1,583
Other		7,135			2,564
Total deferred tax assets		70,629			53,923
Less: Valuation allowance		(70,629	)		(53,923	)
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 (in thousands):

	Balance at Beginning of Year		Charged to Costs and Expenses		Write-offs		Balance at End of Year
Deferred tax valuation allowance:
For year ended December 31, 2013	$	25,047	$	10,965	$	—	$	36,012
For year ended December 31, 2014		36,012		17,911		—		53,923
For year ended December 31, 2015		53,923		16,706		—		70,629

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 R&D credits claimed on the Company’s annual tax return was as follows (in thousands):

	2015		2014		2013
Unrecognized tax benefits at beginning of year	$	777	$	551	$	253
Additions (reductions) based on current year tax positions		264		226		298
Unrecognized tax benefits at end of year	$	1,041	$	777	$	551