Share-Based Compensation - Summary of Share-Based Compensation Expenses (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Summary of share-based compensation expense
Share-based compensation before income tax benefit	$ 1,231	$ 391
Income tax benefit	(462)	(152)
Share-based compensation, net of income tax benefit	769	239
Restricted stock
Summary of share-based compensation expense
Share-based compensation before income tax benefit	594	654
Performance unit incentive plan (“PUP”)
Summary of share-based compensation expense
Share-based compensation before income tax benefit	612	(231)
Restricted stock units
Summary of share-based compensation expense
Share-based compensation before income tax benefit	$ 25	$ (32)