Condensed Consolidating Financial Statements - Condensed Consolidating Statements of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Statement of Income Captions [Line Items]
Net income	$ 31,821	$ 47,565	$ 38,822	$ 21,163	$ 29,203	$ 41,419	$ 35,813	$ 21,594	$ 139,371	$ 128,029	$ 123,160
Other comprehensive income (loss), net of tax:
Amortization of loss on cash flow hedge									862	862	861
Foreign currency translation adjustment									(606)	(2,669)	(1,615)
Other comprehensive income (loss), net of tax									256	(1,807)	(754)
Comprehensive income									139,627	126,222	122,406
Parent
Condensed Statement of Income Captions [Line Items]
Net income									139,371	128,029	123,160
Other comprehensive income (loss), net of tax:
Amortization of loss on cash flow hedge									862	862	861
Foreign currency translation adjustment									(606)	(2,669)	(1,615)
Other comprehensive income (loss), net of tax									256	(1,807)	(754)
Comprehensive income									139,627	126,222	122,406
Guarantor Subsidiaries
Condensed Statement of Income Captions [Line Items]
Net income									17,373	13,163	12,441
Other comprehensive income (loss), net of tax:
Amortization of loss on cash flow hedge									0	0	0
Foreign currency translation adjustment									0	0	0
Other comprehensive income (loss), net of tax									0	0	0
Comprehensive income									17,373	13,163	12,441
Non-Guarantor Subsidiaries
Condensed Statement of Income Captions [Line Items]
Net income									30,059	31,619	33,750
Other comprehensive income (loss), net of tax:
Amortization of loss on cash flow hedge									0	0	0
Foreign currency translation adjustment									(606)	(2,669)	(1,615)
Other comprehensive income (loss), net of tax									(606)	(2,669)	(1,615)
Comprehensive income									29,453	28,950	32,135
Consolidated
Condensed Statement of Income Captions [Line Items]
Net income									139,371	128,029	123,160
Other comprehensive income (loss), net of tax:
Amortization of loss on cash flow hedge									862	862	861
Foreign currency translation adjustment									(606)	(2,669)	(1,615)
Other comprehensive income (loss), net of tax									256	(1,807)	(754)
Comprehensive income									139,627	126,222	122,406
Eliminations
Condensed Statement of Income Captions [Line Items]
Net income									(47,432)	(44,782)	(46,191)
Other comprehensive income (loss), net of tax:
Amortization of loss on cash flow hedge									0	0	0
Foreign currency translation adjustment									606	2,669	1,615
Other comprehensive income (loss), net of tax									606	2,669	1,615
Comprehensive income									$ (46,826)	$ (42,113)	$ (44,576)