Summary of Significant Accounting Policies - Reconciliation of Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Changes in fair value			$ 2,578
Fair value, inputs, level 3
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Common stock warrant liabilities, Beginning balance	$ 687	$ 8,702
Issuance			11,280
Changes in fair value	387	(8,015)	(2,578)
Conversion to common stock	$ (1,074)
Common stock warrant liabilities, Ending balance		$ 687	$ 8,702