Changes in Equity (Rollforward) (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Balances	$ 3,987,508	$ 3,954,925	$ 3,921,241	$ 3,908,351	$ 3,849,528	$ 3,775,989	$ 3,921,241	$ 3,775,989
Dividends declared	(52,592)	(52,591)	(52,585)	(51,778)	(52,751)	(53,504)
Noncontrolling investors of USS	(4,190)	(2,410)	(7,504)	(1,321)
Share repurchases			(106,529)	(114,950)	(93,136)	(84,308)
Equity-based compensation	8,503	8,633	9,429	7,870	8,016	6,695
Net income	104,277	78,765	190,836	152,608	196,746	204,827	373,878	554,181
Other comprehensive loss, net of tax	(121)	186	37	(39)	(52)	(171)	102	(262)
Balances	4,043,385	3,987,508	3,954,925	3,900,741	3,908,351	3,849,528	4,043,385	3,900,741
Common Stock
Balances	646	646	646	645	645	645	646	645
Balances	646	646	646	645	645	645	646	645
Treasury Stock
Balances	(1,623,855)	(1,624,808)	(1,525,113)	(1,354,157)	(1,261,837)	(1,184,243)	(1,525,113)	(1,184,243)
Share repurchases			(106,529)	(114,950)	(93,136)	(84,308)
Equity-based compensation	50	953	6,834	29	816	6,714
Balances	(1,623,805)	(1,623,855)	(1,624,808)	(1,469,078)	(1,354,157)	(1,261,837)	(1,623,805)	(1,469,078)
Additional Paid-In Capital
Balances	1,191,614	1,183,776	1,181,012	1,167,505	1,160,139	1,160,048	1,181,012	1,160,048
Equity-based compensation	8,614	7,838	2,764	8,007	7,366	91
Balances	1,200,228	1,191,614	1,183,776	1,175,512	1,167,505	1,160,139	1,200,228	1,175,512
Retained Earnings
Balances	4,576,629	4,553,882	4,419,296	4,250,419	4,109,034	3,958,320	4,419,296	3,958,320
Dividends declared	(52,592)	(52,591)	(52,585)	(51,778)	(52,751)	(53,504)
Equity-based compensation	(161)	(158)	(169)	(166)	(166)	(110)
Net income	100,143	75,496	187,340	151,048	194,302	204,328
Balances	4,624,019	4,576,629	4,553,882	4,349,523	4,250,419	4,109,034	4,624,019	4,349,523
Accumulated Other Comprehensive Income (Loss)
Balances	216	30	(7)	78	130	301	(7)	301
Other comprehensive loss, net of tax	(121)	186	37	(39)	(52)	(171)
Balances	95	216	30	39	78	130	95	39
Noncontrolling Interests
Balances	(157,742)	(158,601)	(154,593)	(156,139)	(158,583)	(159,082)	(154,593)	(159,082)
Noncontrolling investors of USS	(4,190)	(2,410)	(7,504)	(1,321)
Net income	4,134	3,269	3,496	1,560	2,444	499
Balances	(157,798)	(157,742)	(158,601)	(155,900)	(156,139)	(158,583)	(157,798)	(155,900)
Redeemable Noncontrolling Interest
Balances	152,414	151,014	143,614	139,930	139,930	111,240	143,614	111,240
Noncontrolling investors of USS						28,690
Noncontrolling investors of USS	3,000	1,400	7,400	3,684
Balances	$ 155,414	$ 152,414	$ 151,014	$ 143,614	$ 139,930	$ 139,930	$ 155,414	$ 143,614