Share-Based Compensation - Summary of Share-Based Compensation Expenses (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Summary of share-based compensation expense
Share-based compensation before income tax benefit	$ 875	$ 1,112	$ 2,106	$ 1,503
Income tax benefit	(325)	(417)	(792)	(569)
Share-based compensation, net of income tax benefit	550	695	1,314	934
Restricted stock
Summary of share-based compensation expense
Share-based compensation before income tax benefit	506	759	1,100	1,413
Performance unit incentive plan (“PUP”)
Summary of share-based compensation expense
Share-based compensation before income tax benefit	376	326	988	95
Restricted stock units
Summary of share-based compensation expense
Share-based compensation before income tax benefit	$ (7)	$ 27	$ 18	$ (5)