Segments (Schedule Of Company's Segment Results) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Segment Reporting Information [Line Items]
Revenue, Net	$ 140,160	$ 134,213	$ 134,213	$ 111,005	$ 106,547	$ 111,655	$ 111,437	$ 104,202	$ 519,591	$ 433,841	$ 354,073
Operating income	54,232	61,723	59,892	50,487	23,774	49,062	50,557	47,100	226,334	170,493	146,045
Depreciation and amortization									36,171	33,745	28,368
Capital expenditures									13,454	11,194	9,677
Long-lived assets (excluding goodwill)	378,018				263,469				378,018	263,469
North America [Member]
Segment Reporting Information [Line Items]
Revenue, Net									348,784	287,794	227,373
Operating income									153,687	106,745	91,715
Depreciation and amortization									19,845	20,220	15,990
Capital expenditures									6,840	6,891	5,097
Long-lived assets (excluding goodwill)	113,030				113,192				113,030	113,192
International [Member]
Segment Reporting Information [Line Items]
Revenue, Net									170,807	146,047	126,700
Operating income									72,647	63,748	54,330
Depreciation and amortization									16,326	13,525	12,378
Capital expenditures									6,614	4,303	4,580
Long-lived assets (excluding goodwill)	$ 264,988				$ 150,277				$ 264,988	$ 150,277