Segment Information (Details) (USD $) In Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Segment Reporting Information [Line Items]
Revenues	$ 217,210	$ 156,492	$ 618,710	$ 460,524
Income from operations	56,023	38,512	146,391	106,491
Depreciation and amortization	16,623	12,506	48,781	37,406
Interest expense	(10,573)	(5,474)	(30,765)	(16,247)
Interest income	853	703	2,486	1,597
Provision for income taxes	12,287	12,109	32,192	33,817
Expenditures for additions to property & equipment, net of grants from outside parties	37,248	21,831	87,613	32,444
North American & European Operations [Member]
Segment Reporting Information [Line Items]
Revenues	145,807	124,647	417,449	368,887
Income from operations	37,963	33,604	98,635	88,768
Depreciation and amortization	11,932	10,861	34,843	32,684
Interest expense	(5,988)	(5,472)	17,879	16,245
Interest income	708	116	2,215	227
Provision for income taxes	8,196	10,459	21,753	28,151
Expenditures for additions to property & equipment, net of grants from outside parties	12,054	17,408	33,865	23,285
Australian Operations [Member]
Segment Reporting Information [Line Items]
Revenues	71,403	31,845	201,261	91,637
Income from operations	18,060	4,908	47,756	17,723
Depreciation and amortization	4,691	1,645	13,938	4,722
Interest expense	(4,585)	(2)	12,886	2
Interest income	145	587	271	1,370
Provision for income taxes	4,091	1,650	10,439	5,666
Expenditures for additions to property & equipment, net of grants from outside parties	$ 25,194	$ 4,423	$ 53,748	$ 9,159