Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Summary of components of the provision for income taxes

The components of the provision for income taxes for the year ended December 31, 2017, 2016 and 2015, are as follows (in thousands):

	Year Ended December 31,
	2017		2016		2015
Current:
Federal	$	—	$	—	$	(7)
State		5		—		(22)
Foreign		1,204		—		—
Total current		1,209		—		(29)
Deferred:
Federal		(30)		—		—
State		—		—		—
Foreign		—		—		—
Total deferred		(30)		—		—
Provision for (benefit from) income taxes	$	1,179	$	—	$	(29)

Reconciliation of Statutory Federal Income Tax Rate to the Company's Effective Tax Rate

	December 31,
	2017		2016		2015
Income tax at the federal statutory rate	35.0	%	35.0	%	35.0	%
State taxes, net of federal benefit	0.5		0.3		(3.8)
Net impact related to foreign subsidiary	(1.2)		—		—
Change in valuation allowance	19.9		(36.2)		(30.7)
Impact of tax reform rate change	(56.4)		—		—
Tax credits	1.0		0.3		1.3
Other	(0.7)		0.6		(1.7)
Income tax provision	(1.9)	%	—	%	0.1	%

Significant Components of the Company's Deferred Tax Assets

	December 31,
	2017		2016
	(in thousands)
Deferred tax assets:
Fixed assets and intangibles	$	30,804	$	—
Net operating loss carryforwards		22,355		68,639
Research credits		5,209		2,643
Stock-based compensation		3,159		2,583
Other		754		1,558
Gross deferred tax assets		62,281		75,423
Valuation allowance		(61,911)		(74,520)
Deferred tax assets net of valuation allowance		370		903
Deferred tax liabilities		(370)		(903)
Net deferred tax assets	$	—	$	—

Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits

	December 31,
	2017		2016		2015
	(in thousands)
Balance at beginning of year	$	3,892	$	3,298	$	2,815
Additions (subtractions) based on tax positions related to prior year		16,103		45		(58)
Additions based on tax positions related to current year		739		549		541
Balance at end of year	$	20,734	$	3,892	$	3,298