Share-Based Compensation - Summary of Share-Based Compensation Expenses (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Summary of share-based compensation expense
Share-based compensation before income tax benefit	$ 2,930	$ 5,221	$ 7,232
Income tax benefit	(1,102)	(1,936)	(2,574)
Total share-based compensation, net of income tax benefit	1,828	3,285	4,658
Restricted stock/performance-based restricted stock (PBRS)
Summary of share-based compensation expense
Share-based compensation before income tax benefit	2,495	3,073	3,267
Performance unit incentive plan (PUP)
Summary of share-based compensation expense
Share-based compensation before income tax benefit	359	1,864	2,922
Restricted Stock Units and Performance Based Restricted Stock Units
Summary of share-based compensation expense
Share-based compensation before income tax benefit	76	177	450
Stock options
Summary of share-based compensation expense
Share-based compensation before income tax benefit	$ 0	$ 107	$ 593