Condensed Consolidating Financial Statements - Condensed Consolidating Statements of Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Statement of Income Captions [Line Items]
Net income	$ 25,285	$ 39,365	$ 35,400	$ 23,110	$ 23,443	$ 38,716	$ 31,807	$ 19,743	$ 123,160	$ 113,709	$ 121,613
Other comprehensive income (loss), net of tax:
Amortization of loss on cash flow hedge									861	862	862
Foreign currency translation adjustment									(1,615)	(2,863)	237
Amortization of pension related costs, net of tax:
Actuarial loss									0	0	80
Settlement of pension plan									0	0	1,406
Other comprehensive income (loss), net of tax									(754)	(2,001)	2,585
Comprehensive income									122,406	111,708	124,198
Parent [Member]
Condensed Statement of Income Captions [Line Items]
Net income									123,160	113,709	121,613
Other comprehensive income (loss), net of tax:
Amortization of loss on cash flow hedge									861	862	862
Foreign currency translation adjustment									(1,615)	(2,863)	237
Amortization of pension related costs, net of tax:
Actuarial loss											80
Settlement of pension plan											1,406
Other comprehensive income (loss), net of tax									(754)	(2,001)	2,585
Comprehensive income									122,406	111,708	124,198
Guarantor Subsidiaries [Member]
Condensed Statement of Income Captions [Line Items]
Net income									12,441	12,745	9,472
Other comprehensive income (loss), net of tax:
Amortization of loss on cash flow hedge									0	0	0
Foreign currency translation adjustment									0	0	5
Amortization of pension related costs, net of tax:
Actuarial loss											80
Settlement of pension plan											1,406
Other comprehensive income (loss), net of tax									0	0	1,491
Comprehensive income									12,441	12,745	10,963
Non-Guarantor Subsidiaries [Member]
Condensed Statement of Income Captions [Line Items]
Net income									32,104	34,617	46,774
Other comprehensive income (loss), net of tax:
Amortization of loss on cash flow hedge									0	0	0
Foreign currency translation adjustment									(1,615)	(2,863)	224
Amortization of pension related costs, net of tax:
Actuarial loss											0
Settlement of pension plan											0
Other comprehensive income (loss), net of tax									(1,615)	(2,863)	224
Comprehensive income									30,489	31,754	46,998
Eliminations [Member]
Condensed Statement of Income Captions [Line Items]
Net income									(44,545)	(47,362)	(56,246)
Other comprehensive income (loss), net of tax:
Amortization of loss on cash flow hedge									0	0	0
Foreign currency translation adjustment									1,615	2,863	(229)
Amortization of pension related costs, net of tax:
Actuarial loss											(80)
Settlement of pension plan											(1,406)
Other comprehensive income (loss), net of tax									1,615	2,863	(1,715)
Comprehensive income									(42,930)	(44,499)	(57,961)
Consolidated [Member]
Condensed Statement of Income Captions [Line Items]
Net income									123,160	113,709	121,613
Other comprehensive income (loss), net of tax:
Amortization of loss on cash flow hedge									861	862	862
Foreign currency translation adjustment									(1,615)	(2,863)	237
Amortization of pension related costs, net of tax:
Actuarial loss											80
Settlement of pension plan											1,406
Other comprehensive income (loss), net of tax									(754)	(2,001)	2,585
Comprehensive income									$ 122,406	$ 111,708	$ 124,198