Quarterly Financial Data (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2010		Sep. 30, 2010		Jun. 30, 2010		Mar. 31, 2010		Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Revenues	$ 586,568		$ 572,999		$ 576,774		$ 579,699		$ 571,251		$ 533,165		$ 555,273		$ 530,863		$ 2,316,040	$ 2,190,552	$ 2,053,520
Costs and expenses	(456,551)		(465,949)		(461,751)		(453,253)		(446,331)		(430,518)		(445,975)		(418,505)		(1,837,504)	(1,741,329)	(1,632,125)
Gross profits	130,017		107,050		115,023		126,446		124,920		102,647		109,298		112,358		478,536	449,223	421,395
Operating income	107,825		78,186		80,495		97,193		103,998		68,496		95,926		85,626		363,699	354,046	323,887
Income from continuing operations before income taxes (1)	72,773	[1]	44,042	[1]	44,827	[1]	63,994	[1]	71,972	[1]	28,621	[1]	67,425	[1]	51,441	[1]	225,636	219,459	199,368
Provision for income taxes	(28,223)		(9,027)		(18,089)		(24,065)		(35,203)		(9,941)		(27,198)		(20,116)		79,404	92,458	76,275
Net income	44,550		35,015		26,738		39,929		36,769		18,680		40,227		31,325		146,232	127,001	123,093
Net income attributable to noncontrolling interests	0		481		(645)		(1,165)		(314)		85		58		(413)		(1,329)	(584)	5
Net income attributable to common stockholders	$ 44,550		$ 35,496		$ 26,093		$ 38,764		$ 36,455		$ 18,765		$ 40,285		$ 30,912		$ 144,903	$ 126,417	$ 123,098
Basic — EPS	$ 0.20	[2]	$ 0.15	[2]	$ 0.11	[2]	$ 0.16	[2]	$ 0.15	[2]	$ 0.08	[2]	$ 0.16	[2]	$ 0.12	[2]	$ 0.62	$ 0.51	$ 0.49
Diluted - EPS	$ 0.20	[2]	$ 0.15	[2]	$ 0.11	[2]	$ 0.16	[2]	$ 0.15	[2]	$ 0.08	[2]	$ 0.16	[2]	$ 0.12	[2]	$ 0.61	$ 0.50	$ 0.49

[1] Includes (losses) gains on divestitures and impairment charges, net, as described in Note 20.

[2] Net income per share is computed independently for each of the quarters presented. Therefore, the sum of the quarters’ net income per share may not equal the total computed for the year.