CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interest
Beginning Balance at Dec. 31, 2011	$ 1,227,251	$ 847	$ 0	$ 1,243,303	$ (45,984)	$ 29,085
Beginning Balance (in shares) at Dec. 31, 2011		84,696,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	269,941			267,996		1,945
Currency translation adjustment	6,801				6,292	509
Change in qualifying cash flow hedge, net of tax	628				628
Issuance of common stock for exercise of options, restricted stock units and employee stock purchases (in shares)		1,855,000
Issuance of common stock for exercise of options, restricted stock units and employee stock purchases	68,463	19	68,444
Purchase/ cancellation of treasury stock (in shares)		(563,000)
Purchase/ cancellation of treasury stock	(48,028)	(6)	0	(48,022)
Stock compensation expense	16,339		16,339
Excess tax benefit of stock options exercised	30,161		30,161
Noncontrolling interests attributable to acquisitions	4,386					4,386
Reduction to noncontrolling interests due to additional ownership	(18,039)		1,958			(19,997)
Payments to noncontrolling interests	(580)		(182)			(398)
Ending Balance at Dec. 31, 2012	1,557,323	860	116,720	1,463,277	(39,064)	15,530
Ending Balance (in shares) at Dec. 31, 2012	85,987,883	85,988,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	153,665			152,661		1,004
Currency translation adjustment	(40,619)				(39,657)	(962)
Change in qualifying cash flow hedge, net of tax	157				157
Issuance of common stock for exercise of options, restricted stock units and employee stock purchases (in shares)		548,000
Issuance of common stock for exercise of options, restricted stock units and employee stock purchases	27,135	5	27,130
Purchase/ cancellation of treasury stock (in shares)	(615,210)	(615,000)
Purchase/ cancellation of treasury stock	(66,175)	(6)	0	(66,169)
Stock compensation expense	7,943		7,943
Excess tax benefit of stock options exercised	8,373		8,373
Noncontrolling interests attributable to acquisitions	2,659					2,659
Reduction to noncontrolling interests due to additional ownership	(1,018)		(205)			(813)
Ending Balance at Jun. 30, 2013	$ 1,649,443	$ 859	$ 159,961	$ 1,549,769	$ (78,564)	$ 17,418
Ending Balance (in shares) at Jun. 30, 2013	85,920,543	85,921,000