Income Taxes (Effective Tax Rates) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Effective tax rates differing from U.S. federal statutory rate
U.S. Federal taxes (Benefit) at statutory rate	$ (24,375)	$ (1,747)
State tax expense	(2,428)	(294)
Research and development credits	(751)	(530)
Stock-based compensation	1,683	755
Mark to market fair value adjustments	504	566
Other nondeductible items	841	414
Change in valuation allowance	$ 24,526	851
Provision for income taxes		$ 15
U.S. Federal taxes (Benefit) at statutory rate (as a percent)	(34.00%)	(34.00%)
State tax expense (as a percent)	(3.39%)	(5.72%)
Research and development credits (as a percent)	(1.05%)	(10.32%)
Stock-based compensation (as a percent)	2.35%	14.70%
Mark to market fair value adjustments (as a percent)	0.70%	11.01%
Other nondeductible items (as a percent)	1.17%	8.05%
Change in valuation allowance (as a percent)	34.21%	16.57%
Provision for income taxes (as a percent)		0.29%
State income tax expense		$ 15