Fair Value Measurements - Warrant Liability (Details) - Warrant liability - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Change in fair value using significant unobservable inputs (Level 3):
Balance at beginning of period	$ 5,569	$ 2,783
Adjustments to fair value measurement	(639)	2,786
Conversion upon initial public offering	$ (4,930)
Balance at end of period		$ 5,569