Significant Accounting Policies - Reconciliation of Warrant Liability (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Reconciliation of warrant liability
Fair value of shareholder notes payable	$ 7,500		$ 7,500
Warrants
Reconciliation of warrant liability
Balance at beginning of period	3,072	$ 1,474
Exercise of common stock warrants	(739)
Remeasurement of common stock warrants	(796)	529
Balance at end of period	$ 1,537	$ 2,003