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 [Member]
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		85,988,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	313,084			311,372		1,712
Currency translation adjustment	(19,160)				(17,718)	(1,442)
Change in qualifying cash flow hedge, net of tax	314				314
Issuance of common stock for exercise of options, restricted stock units and employee stock purchases (in shares)		973,000
Issuance of common stock for exercise of options, restricted stock units and employee stock purchases	48,001	10	47,991
Purchase/ cancellation of treasury stock (in shares)		(1,461,000)
Purchase/ cancellation of treasury stock	(163,700)	(15)	0	(163,685)
Stock compensation expense	17,457		17,457
Excess tax benefit of stock options exercised	17,153		17,153
Noncontrolling interests attributable to acquisitions	4,211					4,211
Reduction to noncontrolling interests due to additional ownership	(7,137)		(4,211)			(2,926)
Payments to noncontrolling interests	(8)					(8)
Ending Balance at Dec. 31, 2013	1,767,538	855	195,110	1,610,964	(56,468)	17,077
Ending Balance (in shares) at Dec. 31, 2013	85,500,037	85,500,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	328,146			326,456		1,690
Currency translation adjustment	(82,871)				(80,221)	(2,650)
Change in qualifying cash flow hedge, net of tax	(1,730)				(1,730)
Issuance of common stock for exercise of options, restricted stock units and employee stock purchases (in shares)		1,061,000
Issuance of common stock for exercise of options, restricted stock units and employee stock purchases	58,562	11	58,551
Purchase/ cancellation of treasury stock (in shares)		(1,677,000)
Purchase/ cancellation of treasury stock	(194,066)	(17)	0	(194,049)
Stock compensation expense	17,773		17,773
Excess tax benefit of stock options exercised	17,906		17,906
Noncontrolling interests attributable to acquisitions	6,781					6,781
Reduction to noncontrolling interests due to additional ownership	(854)		(129)			(725)
Ending Balance at Dec. 31, 2014	$ 1,917,185	$ 849	$ 289,211	$ 1,743,371	$ (138,419)	$ 22,173
Ending Balance (in shares) at Dec. 31, 2014	84,883,517	84,884,000