Reconciliation of Income (Loss) from Continuing Operations, Income (Loss) from Discontinued Operations and Net Income (Loss) and Weighted Average Common Shares Outstanding for Calculating Basic Earnings (Loss) Per Share (Details) (USD $)
In Thousands, except Per Share data, unless otherwise specified
 3 Months Ended 9 Months Ended
Sep. 30, 2014
Sep. 30, 2013
Sep. 30, 2014
Sep. 30, 2013
Earnings Per Share [Abstract]        
Income from continuing operations $ 156,608 $ 149,909 $ 335,895 $ 309,723
Income (loss) from discontinued operations, net of tax (4,423) 756 (6,288) (152)
Net income 152,185 150,665 329,607 309,571
Less: Distributed earnings to common shareholders 55,664 50,007 161,439 99,929
Less: Distributed earnings to participating securities 17 19 49 41
Undistributed earnings 96,504 100,639 168,119 209,601
Undistributed earnings allocated to common shareholders 96,478 100,598 168,070 209,520
Undistributed earnings allocated to participating securities 26 41 49 81
Total income from continuing operations available to common shareholders, basic 156,565 149,849 335,797 309,601
Total income available to common shareholders, basic $ 152,142 $ 150,605 $ 329,509 $ 309,449
Weighted-average common shares outstanding, basic 178,992 177,965 178,800 177,671
Basic earnings per share:        
Income from continuing operations $ 0.87 [1],[2] $ 0.84 [1],[2] $ 1.88 [1],[2] $ 1.74 [1],[2]
Income (loss) from discontinued operations, net of tax $ (0.02) [1],[2] $ 0.00 [1],[2] $ (0.04) [1],[2] $ 0.00 [1],[2]
Net income $ 0.85 [1],[2] $ 0.85 [1],[2] $ 1.84 [1],[2] $ 1.74 [1],[2]
[1] Amounts may not sum due to rounding
[2] Earnings per share amounts are computed independently for income from continuing operations, income (loss) from discontinued operations and net income. As a result, the sum of per-share amounts from continuing operations and discontinued operations may not equal the total per-share amount for net income.