Earnings Per Share Level 4 (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
Net Income (Loss) Attributable to Parent [Abstract]                      
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
After tax interest on convertible debt                 51 51 51
Net income — diluted                 $ 144,954 $ 126,468 $ 123,149
Weighted average shares (denominator):                      
Weighted average shares — basic                 (234,242) (248,871) (251,709)
Stock options                 2,306 1,610 654
Convertible debt                 121 121 121
Weighted average shares — diluted                 236,669 250,602 252,484
Net income attributable to common stockholders, basic $ 0.20 [1] $ 0.15 [1] $ 0.11 [1] $ 0.16 [1] $ 0.15 [1] $ 0.08 [1] $ 0.16 [1] $ 0.12 [1] $ 0.62 $ 0.51 $ 0.49
Net income attributable to common stockholders, diluted $ 0.20 [1] $ 0.15 [1] $ 0.11 [1] $ 0.16 [1] $ 0.15 [1] $ 0.08 [1] $ 0.16 [1] $ 0.12 [1] $ 0.61 $ 0.50 $ 0.49
[1] 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.