Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Significant components deferred tax assets

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

	December 31,
	2017			2016			2015
Deferred tax assets:
Capitalized research and development and other	$	7,379		$	9,380		$	33,894
Valuation allowance	(7,379		)	(9,380		)	(33,894		)
Net deferred tax assets	$	—		$	—		$	—

Provision for income taxes

The difference between the provision for income taxes and income taxes computed using the effective U.S. federal statutory rate is as follows (in thousands):

	December 31,
	2017			2016			2015
Income tax benefit at statutory federal rate	$	(39,033	)	$	(26,583	)	$	(14,250	)
Research and development credits	(2,691		)	(1,240		)	1,128
Foreign rate differential	1,249			—			—
Expired tax attributes	2,228			(5		)	31
Impact of the 2017 Tax Act	71,199			—			—
Stock-based compensation	2,253			—			—
Change in valuation allowance	(35,246		)	25,091			12,042
Other permanent differences	41			2,737			1,049
Provision for income taxes	$	—		$	—		$	—