Stock-Based Compensation - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Stock-based compensation
Total stock-based compensation	$ 2,841	$ 1,822	$ 4,704	$ 3,755
Stock options
Stock-based compensation
Total unrecognized compensation cost related to unvested stock-based compensation	1,200		1,200
RSUs
Stock-based compensation
Total unrecognized compensation cost related to unvested stock-based compensation	2,000		2,000
Unvested RSAs
Stock-based compensation
Total unrecognized compensation cost related to unvested stock-based compensation	11,300		11,300
Research and development
Stock-based compensation
Total stock-based compensation	172	232	347	467
General and administrative
Stock-based compensation
Total stock-based compensation	$ 2,669	$ 1,590	$ 4,357	$ 3,288