Share-Based Compensation - Schedule of Activity for Stock Options Granted (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 at beginning of year	3,906,997	3,010,233
Number of shares granted	0	1,272,293
Number of shares exercised		(64,220)
Number of shares forfeited or expired	(374,196)	(311,309)
Number of shares at end of year	3,532,801	3,906,997	3,010,233
Number of shares, exercisable	2,655,687
Number of shares, options expected to vest	863,728
Weighted-average exercise price per share, beginning of year	$ 17.34	$ 21.87
Weighted-average exercise price per share, shares granted		5.69
Weighted-average exercise price per share, share exercised		2.89
Weighted-average exercise price per share, shares forfeited or expired	13.03	16.51
Weighted-average exercise price per share, end of year	17.79	$ 17.34	$ 21.87
Weighted-average exercise price per share, shares exercisable	20.80
Weighted-average exercise price per share, options expected to vest	$ 8.76
Weighted-average remaining contractual term, end of year	4 years 7 months 18 days	5 years 8 months 27 days	5 years 6 months 23 days
Weighted-average remaining contractual term, shares exercisable	3 years 11 months 12 days
Weighted-average remaining contractual term, options expected to vest	6 years 8 months
Aggregate intrinsic value, shares exercised		$ 200
Aggregate intrinsic value, end of year	$ 0	$ 1,809	$ 443
Aggregate intrinsic value, shares exercisable	0
Aggregate intrinsic value, options expected to vest	$ 0