Segment Information (Details) (USD $) In Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Segment Reporting Information [Line Items]
Revenues	$ 209,589	$ 158,453	$ 401,500	$ 304,032
Income from operations	51,165	37,873	90,368	67,979
Depreciation and amortization	16,297	12,452	32,158	24,900
Interest expense	(10,253)	(5,411)	(20,192)	(10,773)
Interest income	858	471	1,633	894
Provision for income taxes	11,420	12,067	19,905	21,708
Expenditures for additions to property & equipment, net of grants from outside parties	42,154	6,385	50,365	10,613
North American & European Operations [Member]
Segment Reporting Information [Line Items]
Revenues	139,335	127,004	271,642	244,240
Income from operations	33,737	31,153	60,672	55,164
Depreciation and amortization	11,565	10,908	22,911	21,823
Interest expense	(5,935)	(5,411)	(11,891)	(10,773)
Interest income	791	56	1,507	111
Provision for income taxes	7,485	9,981	13,557	17,692
Expenditures for additions to property & equipment, net of grants from outside parties	14,742	5,181	21,811	5,877
Australian Operations [Member]
Segment Reporting Information [Line Items]
Revenues	70,254	31,449	129,858	59,792
Income from operations	17,428	6,720	29,696	12,815
Depreciation and amortization	4,732	1,544	9,247	3,077
Interest expense	(4,318)	0	(8,301)	0
Interest income	67	415	126	783
Provision for income taxes	3,935	2,086	6,348	4,016
Expenditures for additions to property & equipment, net of grants from outside parties	$ 27,412	$ 1,204	$ 28,554	$ 4,736