Stock-Based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Options
Outstanding at beginning of period (in shares)	1,073,288
Granted (in shares)	100,000
Exercised (in shares)	(18,333)
Canceled (in shares)	(56,335)
Vested shares expired (in shares)	(65,254)
Outstanding at end of period (in shares)	1,033,366	1,073,288
Vested and expected to vest (in shares)	1,033,366
Exercisable at end of period (in shares)	532,407
Weighted Average Exercise Price
Outstanding at beginning of period (usd per share)	$ 5.26
Granted (usd per share)	2.60
Exercised (usd per share)	2.25
Canceled (usd per share)	2.45
Vested shares expired (usd per share)	33.68
Outstanding at end of period (usd per share)	3.41	$ 5.26
Vested and expected to vest (usd per share)	3.41
Exercisable at end of period (usd per share)	$ 4.33
Weighted Average Remaining Contractual Term (in years)
Weighted average remaining contractual term (in years)	8 years 9 months 18 days	9 years 4 months 24 days
Vested and expected to vest (in years)	8 years 9 months 18 days
Exercisable at end of period (in years)	8 years 6 months
Outstanding aggregate intrinsic value (in thousands)	$ 0	$ 0
Exercised intrinsic value (in thousands)	0
Exercisable aggregate intrinsic value (in thousands)	$ 0