Condensed, Consolidated Statements of Equity (Unaudited) (USD $) In Thousands	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Loss (Income)	Noncontrolling Interests	Noncontrolling Interest [Member]
Beginning Balances at Dec. 31, 2011	$ 1,117,952	$ 87	$ 361,715	$ 745,658	$ 418	$ 10,074
Beginning Balances, shares at Dec. 31, 2011		86,796
Net income	70,797	0	0	69,565	0	1,232
Foreign currency translation adjustment	(413)
Other Comprehensive Income (Loss), Net of Tax	(413)	0	0	0	(413)	0
Distribution to noncontrolling interests	(554)	0	0	0	0	(635)	(635)
Share-based compensation	7,767	0	7,767	0	0	0
Issuance of common stock under stock incentive plans	2,191	1	2,190	0	0	0
Stock Repurchased During Period, Shares		(163)
Stock Issued During Period, Shares, Acquisitions		473
Stock Issued During Period, Value, Acquisitions	10,500	0	10,500	0	0	0
Issuance of common stock under stock incentive plans, shares		635
Stock repurchases	(2,805)	0	(2,805)	0	0	0
Excess tax benefit from stock options	248	0	248	0	0	0
Tax shortfall and other from stock options and awards	9	0	9	0	0	0
Ending Balances at Jun. 30, 2012	1,205,611	88	379,624	815,223	5	10,671
Ending Balances, shares at Jun. 30, 2012		87,741
Beginning Balances at Dec. 31, 2012	1,194,393	88	390,359	791,209	1,847	10,890
Beginning Balances, shares at Dec. 31, 2012		88,372
Net income	73,363	0	0	72,147	0	1,216
Foreign currency translation adjustment	(6,341)
Other Comprehensive Income (Loss), Net of Tax	(6,341)	0	0	0	(6,341)	0
Distribution to noncontrolling interests	(976)	0	0	0	0	(850)	(850)
Adjustments to Additional Paid in Capital, Purchase of Noncontrolling Interest		0		0	0	(469)
Purchase of noncontrolling interests	658					4,082	4,551
Share-based compensation	7,419	0	7,419	0	0	0
Issuance of common stock under stock incentive plans	4,181	1	4,180	0	0	0
Stock Repurchased and Retired During Period, Shares		327
Stock Repurchased and Retired During Period, Value	7,956	0	7,956	0	0	0
Issuance of common stock under stock incentive plans, shares		560
Excess tax benefit from stock options	771	0	771	0	0	0
Ending Balances at Jun. 30, 2013	$ 1,260,429	$ 89	$ 394,304	$ 863,356	$ (4,494)	$ 7,174
Ending Balances, shares at Jun. 30, 2013		88,605