Income Taxes (Tables)

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Summary of Domestic and Foreign Components of Loss Before Income Taxes

The domestic and foreign components of loss before income taxes were as follows (in thousands):

	December 31,
	2018			2017			2016
Domestic	$	(65,695	)	$	(54,568	)	$	(71,672	)
Foreign		(3,194	)		—			—
Loss before income taxes	$	(68,889	)	$	(54,568	)	$	(71,672	)

Summary of Benefit for Income Taxes

The benefit for income taxes consisted of the following (in thousands):  

	Year Ended December 31,
	2018		2017		2016
Benefit for income taxes:
Current:
Federal	$	—	$	—	$	—
State		—		—		—
Foreign		—		—		—
Subtotal		—		—		—
Deferred:
Federal		—		—		(12	)
State		—		—		(2	)
Foreign		—		—		—
Subtotal		—		—		(14	)
Income tax benefit	$	—	$	—	$	(14	)

Schedule of Difference Between Benefit for Income Taxes and Federal Statutory Income Tax Rate

The difference between the benefit for income taxes and the amount computed by applying the federal statutory income tax rate (21%) to loss before taxes is explained as follows (in thousands):

	Year Ended December 31,
	2018			2017			2016
Tax at federal statutory rate	$	(14,467	)	$	(18,553	)	$	(24,369	)
State taxes, net		(2,849	)		795			(747	)
Federal rate change		—			53,045			—
Foreign rate differential		(177	)		—			—
Non-deductible stock-based compensation		(2,729	)		2,120			2,781
Research credits		(1,005	)		(869	)		(1,424	)
Change in valuation allowance		20,271			(36,575	)		23,773
Other		956			37			(28	)
Income tax benefit	$	—		$	—		$	(14	)

Note:

(1) For the years ended December 31, 2016 and 2017 the statutory tax rate was 34%. For the year ended December 31, 2018, as a result of Tax Reform, the statutory tax rate was decreased to 21%.

Schedule of Company's Deferred Tax Assets

Significant components of the Company’s deferred tax assets are as follows (in thousands):

	December 31 ,
	2018			2017
Assets:
Deferred tax assets:
Net operating loss carryforwards	$	138,896		$	91,308
Research and development tax credit carryforwards		16,829			15,147
Stock-based compensation		3,801			3,168
Deferred revenue		3,191			934
Build to suit lease liability		6,400			5,232
Other		604			366
Total deferred tax asset		169,721			116,155
Valuation allowance		158,150			112,833
Net deferred tax assets	$	11,571		$	3,322
Liabilities:
Intangible assets		(14,100	)		—
Fixed Assets		(4,176	)		(3,322	)
Net deferred tax liability		(18,276	)		(3,322	)
Total deferred tax liability	$	(6,705	)	$	—

Summary of Activity Related to Company's Unrecognized Tax Benefits

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

	December 31,
	2018			2017			2016
Beginning balance	$	5,659		$	5,045		$	8,330
Additions based on tax positions related to the current year		636			622			1,023
Additions for tax positions of prior years		(7	)		(8	)		27
Reductions for tax positions of prior years		—			—			(4,335	)
Ending balance	$	6,288		$	5,659		$	5,045