Warrants - Aggregate Fair Values, Inputs and Assumptions (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Fair value assumptions
Proceeds from Series A preferred stock offering allocated to warrants	$ 7,623	$ 0
Proceeds recorded in Additional paid-in capital	7,623
Additional paid-in capital
Fair value assumptions
Proceeds recorded in Additional paid-in capital	$ 7,623
Warrant
Fair value assumptions
Volatility	89.69%
Weighted average remaining expected life	5 years
Interest rate (as a percent)	2.08%
Dividend yield	0.00%
Proceeds from Series A preferred stock offering allocated to warrants	$ 3,000
Warrant
Fair value assumptions
Calculated aggregate value	$ 15,716		$ 6,034
Weighted average exercise price per share (usd per share)	$ 6.00		$ 5.98
Closing price per share of common stock (usd per share)	$ 4.01		$ 1.89
Volatility	85.50%		85.60%
Weighted average remaining expected life	3 years 9 months		4 years 3 months
Interest rate (as a percent)	1.68%		1.75%
Dividend yield	0.00%		0.00%