Share-Based Compensation - Summary of Share-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Summary of share-based compensation expense
Share-based compensation before income tax benefit	$ 4,737	$ 2,210	$ 9,484	$ 4,709
Income tax benefit	(1,752)	(812)	(3,524)	(1,750)
Share-based compensation, net of income tax benefit	2,985	1,398	5,960	2,959
Performance unit incentive plan (“PUP”)
Summary of share-based compensation expense
Share-based compensation before income tax benefit	3,941	1,601	7,184	2,952
Restricted stock
Summary of share-based compensation expense
Share-based compensation before income tax benefit	672	523	2,069	1,597
Restricted stock units
Summary of share-based compensation expense
Share-based compensation before income tax benefit	$ 124	$ 86	$ 231	$ 160