Segment and Geographic Area Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Segment Reporting Information [Line Items]
Number of Operating Regions									11
Revenues	$ 227,316	$ 222,745	$ 217,419	$ 207,436	$ 210,386	$ 217,210	$ 209,589	$ 191,911	$ 874,916	$ 829,096	$ 630,195
Income from operations	33,660	52,875	62,473	41,314	45,388	56,023	51,165	39,203	190,322	191,779	130,410
Depreciation and amortization									73,405	66,481	51,166
Interest expense									(62,845)	(38,617)	(23,147)
Interest income									3,725	3,243	2,397
Provision for income taxes									(46,402)	(38,531)	(30,164)
Expenditures for additions to property & equipment, net of grants from outside parties									(192,062)	(156,026)	(79,038)
North American & European Operations [Member]
Segment Reporting Information [Line Items]
Revenues									585,893	557,621	494,787
Income from operations									115,387	129,646	119,902
Depreciation and amortization									50,156	47,218	43,807
Interest expense									(45,996)	(23,171)	(21,856)
Interest income									3,219	2,950	485
Provision for income taxes									(28,451)	(26,181)	(27,176)
Expenditures for additions to property & equipment, net of grants from outside parties									(69,636)	(59,383)	(59,153)
Australian Operations [Member]
Segment Reporting Information [Line Items]
Revenues									289,023	271,475	135,408
Income from operations									74,935	62,133	10,508
Depreciation and amortization									23,249	19,263	7,359
Interest expense									(16,849)	(15,446)	(1,291)
Interest income									506	293	1,912
Provision for income taxes									(17,951)	(12,350)	(2,988)
Expenditures for additions to property & equipment, net of grants from outside parties									$ (122,426)	$ (96,643)	$ (19,885)