Share-Based Compensation - Share based Compensation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Summary of share-based compensation
Share-based compensation	$ 1,649	$ 1,687	$ 4,178
Incentive Stock Options (share settled)
Summary of share-based compensation
Share-based compensation	820	206	243
Non-Qualified Stock Options (share settled)
Summary of share-based compensation
Share-based compensation	387	164	71
Restricted stock (share settled)
Summary of share-based compensation
Share-based compensation	197	1,073	4,303
Cash settled stock units
Summary of share-based compensation
Share-based compensation	$ 245	$ 244	$ (439)