Condensed Consolidating Financial Statements Condensed Consolidating Statements of Comprehensive Income (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Net income	$ 23,443,000	$ 38,716,000	$ 31,807,000	$ 19,743,000	$ 20,704,000	$ 42,744,000	$ 34,374,000	$ 23,791,000	$ 113,709,000	$ 121,613,000	$ 111,061,000
Other comprehensive income (loss), net of tax:
Amortization of loss on cash flow hedge									862,000	862,000	862,000
Foreign currency translation adjustment									(2,863,000)	237,000	615,000
Amortization of pension related costs, net of tax:
Actuarial loss									0	80,000	0
Settlement of pension plan									0	1,406,000	0
Actuarial pension loss, net of tax									0	0	(1,086,000)
Other comprehensive income (loss), net of tax									(2,001,000)	2,585,000	391,000
Comprehensive income									111,708,000	124,198,000	111,452,000
Parent [Member]
Net income									113,709,000	121,613,000	111,061,000
Other comprehensive income (loss), net of tax:
Amortization of loss on cash flow hedge									862,000	862,000	862,000
Foreign currency translation adjustment									(2,863,000)	237,000	615,000
Amortization of pension related costs, net of tax:
Actuarial loss										80,000
Settlement of pension plan										1,406,000
Actuarial pension loss, net of tax											(1,086,000)
Other comprehensive income (loss), net of tax									(2,001,000)	2,585,000	391,000
Comprehensive income									111,708,000	124,198,000	111,452,000
Guarantor Subsidiaries [Member]
Net income									12,745,000	9,472,000	14,355,000
Other comprehensive income (loss), net of tax:
Amortization of loss on cash flow hedge									0	0	0
Foreign currency translation adjustment									0	5,000	248,000
Amortization of pension related costs, net of tax:
Actuarial loss										80,000
Settlement of pension plan										1,406,000
Actuarial pension loss, net of tax											(1,086,000)
Other comprehensive income (loss), net of tax									0	1,491,000	(838,000)
Comprehensive income									12,745,000	10,963,000	13,517,000
Non-Guarantor Subsidiaries [Member]
Net income									34,617,000	46,774,000	16,340,000
Other comprehensive income (loss), net of tax:
Amortization of loss on cash flow hedge									0	0	0
Foreign currency translation adjustment									(2,863,000)	224,000	(1,604,000)
Amortization of pension related costs, net of tax:
Actuarial loss										0
Settlement of pension plan										0
Actuarial pension loss, net of tax											0
Other comprehensive income (loss), net of tax									(2,863,000)	224,000	(1,604,000)
Comprehensive income									31,754,000	46,998,000	14,736,000
Eliminations [Member]
Net income									(47,362,000)	(56,246,000)	(30,695,000)
Other comprehensive income (loss), net of tax:
Amortization of loss on cash flow hedge									0	0	0
Foreign currency translation adjustment									2,863,000	(229,000)	1,356,000
Amortization of pension related costs, net of tax:
Actuarial loss										(80,000)
Settlement of pension plan										(1,406,000)
Actuarial pension loss, net of tax											1,086,000
Other comprehensive income (loss), net of tax									2,863,000	(1,715,000)	2,442,000
Comprehensive income									(44,499,000)	(57,961,000)	(28,253,000)
Consolidated [Member]
Net income									113,709,000	121,613,000	111,061,000
Other comprehensive income (loss), net of tax:
Amortization of loss on cash flow hedge									862,000	862,000	862,000
Foreign currency translation adjustment									(2,863,000)	237,000	615,000
Amortization of pension related costs, net of tax:
Actuarial loss										80,000
Settlement of pension plan										1,406,000
Actuarial pension loss, net of tax											(1,086,000)
Other comprehensive income (loss), net of tax									(2,001,000)	2,585,000	391,000
Comprehensive income									$ 111,708,000	$ 124,198,000	$ 111,452,000