Stock-Based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of shares outstanding, beginning balance	1,279,379	1,044,723
Number of shares, granted	295,000	528,479
Number of shares, expired	(211,773)	(11,840)
Number of shares, forfeited	(273,093)	(281,983)
Number of shares outstanding, ending balance	1,089,513	1,279,379	1,044,723
Number of shares, exercisable	665,334
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted-average exercise price, outstanding (usd per share), beginning balance	$ 15.16	$ 18.69
Weighted-average exercise price, granted (usd per share)	2.88	4.80
Weighted-average exercise price, expired (usd per share)	21.35	11.84
Weighted-average exercise price, forfeited (usd per share)	9.50	8.49
Weighted-average exercise price, outstanding (usd per share), ending balance	12.06	$ 15.16	$ 18.69
Weighted-average exercise price, exercisable (usd per share)	$ 17.48
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted-average remaining contractual term (in years), outstanding	7 years 3 months	7 years 2 months	8 years
Weighted-average remaining contractual term (in years), exercisable	6 years 1 month
Aggregate intrinsic value, outstanding	$ 0	$ 0	$ 1,630
Aggregate intrinsic value, exercisable	$ 0