Significant Accounting Policies - Summary of Changes in the Fair Value of the Company's Preferred Stock Warrant Liability (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, Calculation [Roll Forward]
Change in fair value of common stock warrants included in other income (expense)	$ 110	$ 3,104	$ (123)
PIPE Warrants
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	115
Change in fair value of common stock warrants included in other income (expense)	110	3,100
Ending balance	$ 5	$ 115