Business Overview (Details) $ / shares in Units, $ in Thousands		3 Months Ended
	May. 06, 2016 USD ($) $ / shares shares	Mar. 31, 2016 USD ($) item	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of lead product candidates | item		2
Net cash (used in) operating activities		$ (27,552)	$ (23,149)
Cash and cash equivalents		84,155	78,718	$ 61,653	$ 146,470
Loss from operations		27,550	22,804
Working Capital		68,300
Subsequent Event [Line Items]
Net proceeds from private placement		$ 0	$ 5,558
Subsequent Event | Private Placement
Subsequent Event [Line Items]
Shares sold in private placement (in shares) | shares	29,948,334
Shares issued (in dollars per share) | $ / shares	$ 3.00
Net proceeds from private placement	$ 89,700