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.