Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Summary of Significant Accounting Policies
Net (loss) income	$ (35,961)	$ (8,685)
Accumulated deficit	381,809		$ 345,848
Cash and cash equivalents	9,086	$ 33,985	15,256	$ 28,947
Short-term investments	106,692		130,860
Outstanding debt with accrued interest	49,807		49,624
Restricted cash
Restricted cash, current portion	775		1,092
Restricted cash, long term portion	$ 342		$ 342