Income Taxes Income Taxes (Details) 2 - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Income tax benefit at statutory federal rate	$ (14,250)	$ (7,256)	$ (6,098)
Research and development credits	1,128	991	126
Expired tax attributes	31	(60)	0
Change in valuation allowance	12,042	6,322	5,972
Other	1,049	3	0
Provision for income taxes	$ 0	$ 0	$ 0