Stock-Based Compensation - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Stock-based compensation
Total stock-based compensation	$ 1,718	$ 1,468	$ 6,423	$ 5,223
Stock options
Stock-based compensation
Total unrecognized compensation cost related to unvested stock-based compensation	1,000		1,000
RSUs
Stock-based compensation
Total unrecognized compensation cost related to unvested stock-based compensation	1,500		1,500
Unvested RSAs
Stock-based compensation
Total unrecognized compensation cost related to unvested stock-based compensation	10,500		10,500
Research and development
Stock-based compensation
Total stock-based compensation	143	220	490	687
General and administrative
Stock-based compensation
Total stock-based compensation	$ 1,575	$ 1,248	$ 5,933	$ 4,536