Income Taxes (Tables)

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Loss Before Income Taxes

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

	2018			2017			2016
Domestic	$	(78,124	)	$	(44,324	)	$	(47,562	)
Foreign	973			966			589
Loss before income taxes	$	(77,151	)	$	(43,358	)	$	(46,973	)

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):

	2018		2017		2016
Current:
Domestic	$	—	$	—	$	—
Foreign	249		204		116
Total provision for income taxes	$	249	$	204	$	116

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

A reconciliation of the federal statutory income tax rate to the effective income tax rate for the years ended December 31 are as follows (in thousands):

	2018			2017			2016
Income tax provision at statutory rate	$	(16,202	)	$	(15,076	)	$	(16,010	)
Tax on repatriated foreign earnings and other nondeductible items	195			179			135
Change in tax credits	(2,148		)	(2,361		)	(1,449		)
Change in valuation allowance	19,935			(19,792		)	17,824
Change in tax rate	—			37,690			—
Foreign tax and other	(1,531		)	(436		)	(384		)
Total provision for income taxes	$	249		$	204		$	116

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):

	2018			2017
Net operating loss carryforwards	$	63,442		$	49,662
Research and development tax credit carryforwards	8,491			6,505
Foreign tax credit carryforwards	613			448
Stock-based compensation	7,703			5,664
Other	8,347			6,382
Total deferred tax assets	88,596			68,661
Less: Valuation allowance	(88,596		)	(68,661		)
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):

	2018		2017			2016
Balance at beginning of year	$	68,661	$	88,453		$	70,629
Charged to costs and expenses	19,935		17,898			17,824
Impact of change in tax rate	—		(37,690		)	—
Balance at end of year	$	88,596	$	68,661		$	88,453

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):

	2018		2017		2016
Unrecognized tax benefits at beginning of year	$	2,168	$	1,524	$	1,041
Additions based on current year tax positions	662		644		483
Unrecognized tax benefits at end of year	$	2,830	$	2,168	$	1,524