Fair Value Measurements - Reconciliation for liabilities measure at fair value using level 3 (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Liabilities Measured at Fair Value on a Recurring Basis Using Significant Unobservable Inputs (Level 3)
Balance at beginning of period	$ 22,884	$ 1,818
Common stock warrant exercise	(28,996)	(7,298)
Total losses included in earnings	$ 6,112	28,364
Balance at end of period		$ 22,884