Income Taxes (Tables)

12 Months Ended

Dec. 31, 2014

Income Taxes

Schedule of differences between the actual tax provision (benefit) and the tax provision (benefit) computed using the United States federal income tax rate

        Differences between the actual tax provision (benefit) and the tax provision (benefit) computed using the United States federal income tax rate is as follows for the years ended December 31, 2014, 2013 and 2012 (in thousands):

	Years ended December 31,
	2014			2013			2012
Benefit at statutory rate	$	(29,293	)	$	(30,665	)	$	(21,349	)
State taxes, net of federal benefit		(3,342	)		(3,735	)		(3,220	)
State net operating loss expiration		—			661			3,167
Stock-based compensation		1,094			1,118			382
Tax credits		(1,720	)		(2,462	)		(411	)
Foreign rate differential		6,243			5,252			—
Other		100			(47	)		22
Increase in valuation allowance		26,918			29,878			21,409
Income tax provision (benefit)	$	—		$	—		$	—

Schedule of effects of temporary differences that give rise to significant portions of deferred tax assets and deferred tax liabilities

        The effects of temporary differences that give rise to significant portions of deferred tax assets and deferred tax liabilities at December 31, 2014 and 2013 are presented below (in thousands):

	2014			2013
Deferred tax assets:
Federal and state net operating loss carryforwards	$	194,091		$	170,557
Federal and state research and development credits		21,401			19,675
Depreciation and amortization		2,423			2,412
Deferred compensation		7,643			6,254
Other		1,427			1,169
Deferred tax assets		226,985			200,067
Less valuation allowance		(226,985	)		(200,067	)
Net deferred tax assets	$	—		$	—