Condensed Consolidating Financial Statements Condensed Consolidating Statement Of Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Net income	$ 31,862	$ 27,578	$ 51,859	$ 43,308
Amortization of loss on cash flow hedge	216	216	431	431
Foreign currency translation adjustment, net	(432)	498	(20)	1,003
Actuarial loss	20	0	40	0
Actuarial pension loss	0	0	0	(10)
Other comprehensive income (loss), net of tax	(196)	714	451	1,424
Comprehensive income	31,666	28,292	52,310	44,732
Parent [Member]
Net income	31,862	27,578	51,859	43,308
Amortization of loss on cash flow hedge	216	216	431	431
Foreign currency translation adjustment, net	(1)	(5)	14	67
Actuarial loss	0		0
Actuarial pension loss				0
Other comprehensive income (loss), net of tax	215	211	445	498
Comprehensive income	32,077	27,789	52,304	43,806
Guarantor Subsidiaries [Member]
Net income	2,372	3,849	6,673	7,964
Amortization of loss on cash flow hedge	0	0	0	0
Foreign currency translation adjustment, net	(2)	13	4	17
Actuarial loss	20		40
Actuarial pension loss				(10)
Other comprehensive income (loss), net of tax	18	13	44	7
Comprehensive income	2,390	3,862	6,717	7,971
Non-Guarantor Subsidiaries [Member]
Net income	5,793	4,948	8,373	5,906
Amortization of loss on cash flow hedge	0	0	0	0
Foreign currency translation adjustment, net	(428)	568	(26)	1,095
Actuarial loss	0		0
Actuarial pension loss				0
Other comprehensive income (loss), net of tax	(428)	568	(26)	1,095
Comprehensive income	5,365	5,516	8,347	7,001
Eliminations [Member]
Net income	(8,165)	(8,797)	(15,046)	(13,870)
Amortization of loss on cash flow hedge	0	0	0	0
Foreign currency translation adjustment, net	(1)	(78)	(12)	(176)
Actuarial loss	0		0
Actuarial pension loss				0
Other comprehensive income (loss), net of tax	(1)	(78)	(12)	(176)
Comprehensive income	(8,166)	(8,875)	(15,058)	(14,046)
Consolidated [Member]
Net income	31,862	27,578	51,859	43,308
Amortization of loss on cash flow hedge	216	216	431	431
Foreign currency translation adjustment, net	(432)	498	(20)	1,003
Actuarial loss	20		40
Actuarial pension loss				(10)
Other comprehensive income (loss), net of tax	(196)	714	451	1,424
Comprehensive income	$ 31,666	$ 28,292	$ 52,310	$ 44,732