CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (USD $)	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interest
Beginning Balance at Dec. 31, 2010	$ 1,080,350,000	$ 852,000	$ 46,945,000	$ 1,017,497,000	$ (16,869,000)	$ 31,925,000
Beginning Balance (in shares) at Dec. 31, 2010		85,242,000
Net income	237,343,000			234,751,000		2,592,000
Currency translation adjustment	(32,893,000)				(29,456,000)	(3,437,000)
Amortization of treasury lock into income, net of tax of $162 and $216 for the nine months ended September 30,2012 and for the year ended December 31,2011 respectively	341,000				341,000
Comprehensive income	204,791,000
Issuance of common stock for exercise of options and employee stock purchases (in shares)		1,016,000
Issuance of common stock for exercise of options and employee stock purchases	36,405,000	11,000	36,394,000
Purchase/ cancellation of treasury stock (in Shares)		(1,562,000)
Purchase/ cancellation of treasury stock	(124,056,000)	(16,000)	(115,095,000)	(8,945,000)
Stock compensation expense	15,367,000		15,367,000
Excess tax benefit of stock options exercised	17,410,000		17,410,000
Noncontrolling interests acquired from new acquisitions	10,708,000					10,708,000
Reduction to noncontrolling interests due to additional ownership	(11,231,000)		(1,021,000)			(10,210,000)
Reduction to noncontrolling interests due to divestiture	(1,959,000)					(1,959,000)
Payments to noncontrolling interests	(534,000)					(534,000)
Ending Balance at Dec. 31, 2011	1,227,251,000	847,000	0	1,243,303,000	(45,984,000)	29,085,000
Ending Balance (in shares) at Dec. 31, 2011	84,696,227	84,696,227
Net income	199,433,000			197,927,000		1,506,000
Currency translation adjustment	4,437,000				3,837,000	600,000
Amortization of treasury lock into income, net of tax of $162 and $216 for the nine months ended September 30,2012 and for the year ended December 31,2011 respectively	256,000				256,000
Change in fair value of cash flow hedge, net of tax of $193	289,000				289,000
Comprehensive income	204,415,000
Issuance of common stock for exercise of options and employee stock purchases (in shares)		1,311,000
Issuance of common stock for exercise of options and employee stock purchases	48,761,000	13,000	48,748,000
Purchase/ cancellation of treasury stock (in Shares)	(82,052)	(82,000)
Purchase/ cancellation of treasury stock	(6,858,000)	(1,000)	0	(6,857,000)
Stock compensation expense	12,346,000		12,346,000
Excess tax benefit of stock options exercised	20,994,000		20,994,000
Noncontrolling interests acquired from new acquisitions	4,386,000					4,386,000
Reduction to noncontrolling interests due to additional ownership	(18,039,000)		1,958,000			(19,997,000)
Payments to noncontrolling interests	(398,000)					(398,000)
Ending Balance at Sep. 30, 2012	$ 1,492,858,000	$ 859,000	$ 84,046,000	$ 1,434,373,000	$ (41,602,000)	$ 15,182,000
Ending Balance (in shares) at Sep. 30, 2012	85,924,721	85,924,721