Condensed Consolidating Financial Statements Condensed Consolidating Statements of Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011		Dec. 31, 2010
Net income	$ 120,687	$ 110,396		$ 107,441
Settlement of forward starting interest rate swap agreement	0	0		(8,663)
Amortization of loss on cash flow hedge	862	862		332
Foreign currency translation adjustment, net	237	615		1,265
Actuarial loss	80	0		0
Settlement of pension plan	1,406	0		0
Actuarial pension loss, net of tax	0	(1,086)		(459)
Comprehensive income	123,272	110,787		99,916
Parent [Member]
Net income	120,687	110,396		107,441
Settlement of forward starting interest rate swap agreement				(8,663)
Amortization of loss on cash flow hedge	862	862		332
Foreign currency translation adjustment, net	237	615		1,265
Actuarial loss	80
Settlement of pension plan	1,406
Actuarial pension loss, net of tax		(1,086)		(459)
Other comprehensive income (loss), net of tax	2,585	391		(7,525)
Comprehensive income	123,272	110,787		99,916
Guarantor Subsidiaries [Member]
Net income	8,582	14,362		21,059
Settlement of forward starting interest rate swap agreement				0
Amortization of loss on cash flow hedge	0	0		0
Foreign currency translation adjustment, net	5	248		(289)
Actuarial loss	80
Settlement of pension plan	1,406
Actuarial pension loss, net of tax		(1,086)		(459)
Other comprehensive income (loss), net of tax	1,491	(838)		(748)
Comprehensive income	10,073	13,524		20,311
Non-Guarantor Subsidiaries [Member]
Net income	47,252	16,233	[1]	16,020	[1]
Settlement of forward starting interest rate swap agreement				0
Amortization of loss on cash flow hedge	0	0		0
Foreign currency translation adjustment, net	224	(1,604)		11,435
Actuarial loss	0
Settlement of pension plan	0
Actuarial pension loss, net of tax		0		0
Other comprehensive income (loss), net of tax	224	(1,604)		11,435
Comprehensive income	47,476	14,629		27,455
Eliminations [Member]
Net income	(55,834)	(30,595)		(37,079)
Settlement of forward starting interest rate swap agreement				0
Amortization of loss on cash flow hedge	0	0		0
Foreign currency translation adjustment, net	(229)	1,356		(11,146)
Actuarial loss	(80)
Settlement of pension plan	(1,406)
Actuarial pension loss, net of tax		1,086		459
Other comprehensive income (loss), net of tax	(1,715)	2,442		(10,687)
Comprehensive income	(57,549)	(28,153)		(47,766)
Consolidated [Member]
Net income	120,687	110,396		107,441
Settlement of forward starting interest rate swap agreement				(8,663)
Amortization of loss on cash flow hedge	862	862		332
Foreign currency translation adjustment, net	237	615		1,265
Actuarial loss	80
Settlement of pension plan	1,406
Actuarial pension loss, net of tax		(1,086)		(459)
Other comprehensive income (loss), net of tax	2,585	391		(7,525)
Comprehensive income	$ 123,272	$ 110,787		$ 99,916

[1] Refer to Note 1 with regards to the reclassification of foreign revenue.