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.