Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Schedule of Components of Income (Loss) Before Income Taxes

The components of income (loss) before income taxes were as follows:

	Year Ended December 31,
	2017			2016			2015
Foreign	$	(35,680	)	$	(26,928	)	$	(21,409	)
U.S.		(93,241	)		(82,510	)		(96,676	)
Totals	$	(128,921	)	$	(109,438	)	$	(118,085	)

Schedule of Significant Components of Company's Deferred Tax Assets

The significant components of the Company’s deferred tax assets are comprised of the following:

	Year Ended December 31,
	2017			2016
Deferred tax assets:
U.S. and state net operating loss carryforwards	$	84,556		$	91,584
Stock-based compensation		15,748			17,004
Accruals and other temporary differences		2,386			2,491
Research and development credits		29,186			15,898
Capitalized research and development		2,211			3,344
Total deferred tax assets		134,087			130,321
Less valuation allowance		(134,087	)		(130,321	)
Net deferred tax assets	$	—		$	—

Schedule of Reconciliation of Income Tax Expense Computed at Statutory Federal Income Tax Rate to Income Taxes

A reconciliation of income tax expense computed at the statutory federal income tax rate to income taxes as reflected in the financial statements is as follows:

	Year Ended December 31,
	2017			2016			2015
Federal income tax expense at statutory rate		34.0	%		34.0	%		34.0	%
State income tax, net of federal benefit		5.9	%		3.3	%		3.5	%
Permanent differences		(3.9	)%		(3.1	)%		(5.1	)%
Research and development credit		8.4	%		4.8	%		12.2	%
Foreign rate differential		(9.4	)%		(8.5	)%		(6.3	)%
Change in valuation allowance		(1.4	)%		(25.1	)%		(39.4	)%
Provision to return adjustments		1.0	%		(5.5	)%		—	%
Other		(1.4	)%		—	%		1.0	%
Federal rate change		(33.2	)%		—	%		—	%
Effective income tax rate		—	%		(0.1	)%		(0.1	)%