Changes in Equity (Rollforward) (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Balances	$ 3,908,351	$ 3,849,528	$ 3,775,989	$ 3,588,519	$ 3,312,137	$ 3,195,068	$ 3,775,989	$ 3,195,068
Dividends declared	(51,778)	(52,751)	(53,504)	(43,767)	(44,080)	(44,269)
Noncontrolling investors, net	(1,321)				(3)
Share repurchases	(114,950)	(93,136)	(84,308)	(74,965)	(49,145)	(69,269)
Equity-based compensation	7,870	8,016	6,695	7,081	7,143	5,132
Net income	152,608	196,746	204,827	397,906	362,572		554,181	985,953
Other comprehensive loss, net of tax	(39)	(52)	(171)	63	(105)		(262)	(42)
Comprehensive and net income (loss)	152,569			397,969		225,475	553,919	985,911
Balances	3,900,741	3,908,351	3,849,528	3,874,837	3,588,519	3,312,137	3,900,741	3,874,837
Common Stock
Balances	645	645	645	644	644	644	645	644
Balances	645	645	645	644	644	644	645	644
Treasury Stock
Balances	(1,354,157)	(1,261,837)	(1,184,243)	(779,088)	(730,700)	(665,297)	(1,184,243)	(665,297)
Share repurchases	(114,950)	(93,136)	(84,308)	(74,965)	(49,145)	(69,269)
Equity-based compensation	29	816	6,714	1	757	3,866
Balances	(1,469,078)	(1,354,157)	(1,261,837)	(854,052)	(779,088)	(730,700)	(1,469,078)	(854,052)
Additional Paid-In Capital
Balances	1,167,505	1,160,139	1,160,048	1,149,367	1,142,871	1,141,534	1,160,048	1,141,534
Equity-based compensation	8,007	7,366	91	7,189	6,496	1,337
Balances	1,175,512	1,167,505	1,160,139	1,156,556	1,149,367	1,142,871	1,175,512	1,156,556
Retained Earnings
Balances	4,250,419	4,109,034	3,958,320	3,376,163	3,057,904	2,874,693	3,958,320	2,874,693
Dividends declared	(51,778)	(52,751)	(53,504)	(43,767)	(44,080)	(44,269)
Equity-based compensation	(166)	(166)	(110)	(109)	(110)	(71)
Net income	151,048	194,302	204,328	398,375	362,449
Comprehensive and net income (loss)						227,551
Balances	4,349,523	4,250,419	4,109,034	3,730,662	3,376,163	3,057,904	4,349,523	3,730,662
AOCI Attributable to Parent [Member]
Balances	78	130	301	(105)			301
Other comprehensive loss, net of tax	(39)	(52)	(171)	63	(105)
Balances	39	78	130	(42)	(105)		39	(42)
Noncontrolling Interests
Balances	(156,139)	(158,583)	(159,082)	(158,462)	(158,582)	(156,506)	(159,082)	(156,506)
Noncontrolling investors, net	(1,321)				(3)
Net income	1,560	2,444	499	(469)	123
Comprehensive and net income (loss)						(2,076)
Balances	(155,900)	(156,139)	(158,583)	(158,931)	(158,462)	(158,582)	(155,900)	(158,931)
Redeemable Noncontrolling Interest
Balances	139,930	139,930	111,240	111,240	111,240	111,240	111,240	111,240
Noncontrolling investors of USS	3,684		28,690
Balances	$ 143,614	$ 139,930	$ 139,930	$ 111,240	$ 111,240	$ 111,240	$ 143,614	$ 111,240