Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Summary of Significant Accounting Policies
Net loss	$ (8,073)	$ (9,963)	$ (10,193)	$ (11,937)	$ (28,250)	$ (6,604)	$ (2,992)	$ (3,384)	$ (40,166)	$ (41,230)	$ (5,811)
Cash provided by (used in) operations									(34,430)	(18,184)	450
Accumulated deficit	215,442				175,276				215,442	175,276
Cash and cash equivalents	$ 67,212				$ 112,801				$ 67,212	$ 112,801	$ 96,729	$ 9,722