Condensed Consolidated Statements of Changes in Equity (Unaudited) - USD ($) $ in Thousands		Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Parent [Member]	Noncontrolling Interest [Member]	Total
Beginning balance at Dec. 31, 2016		$ (676,867)	$ 5,766	$ 32	$ 4,250	$ 5,922,958	$ 5,256,139	$ 146,735	$ 5,402,874
Balance (in shares) at Dec. 31, 2016				32,000	425,034,000
Contributions/deemed contributions from noncontrolling interests								48,867	48,867
Net income		341,179					341,179	13,926	355,105
Change in unrealized loss on marketable securities			(1,466)				(1,466)		(1,466)
Change in unrealized loss on interest rate swaps			308				308		308
Change in foreign currency translation adjustment			(6,335)				(6,335)		(6,335)
Redeemable noncontrolling interests income								(1,203)	(1,203)
Dividends declared to common and preferred shares		(379,933)					(379,933)		(379,933)
Distributions to noncontrolling interests								(13,513)	(13,513)
Issuance of common stock					$ 8	(8)
Issuance of common stock (in shares)					776,000
Issuance of preferred stock				$ 9		217,566	217,575		217,575
Issuance of preferred stock (in shares)				9,000
Surrender of restricted stock					$ (2)	(5,597)	(5,599)		(5,599)
Surrender of restricted stock (in shares)					(239,000)
Exercise of common stock options						1,174	1,174		1,174
Exercise of common stock options (in shares)					62,000
Amortization of equity awards						15,290	15,290		15,290
Redemption of preferred stock				$ (9)		(224,991)	(225,000)		(225,000)
Redemption of preferred stock (in shares)				(9,000)
Balance (in shares) at Sep. 30, 2017				32,000	425,633,000
Ending balance at Sep. 30, 2017		(715,621)	(1,727)	$ 32	$ 4,256	5,926,392	5,213,332	194,812	5,408,144
Beginning balance at Dec. 31, 2017		(761,337)	(1,480)	$ 41	$ 4,256	6,152,764	5,394,244	127,903	5,522,147
Balance (in shares) at Dec. 31, 2017				41,000	425,646,000
Contributions/deemed contributions from noncontrolling interests								109	109
Net income		409,634					409,634	882	410,516
Change in unrealized loss on marketable securities
Change in unrealized loss on interest rate swaps			344				344		344
Redeemable noncontrolling interests income								(279)	(279)
Dividends declared to common and preferred shares		(398,605)					(398,605)		(398,605)
Distributions to noncontrolling interests								(2,373)	(2,373)
Issuance of common stock					$ 11	(11)
Issuance of common stock (in shares)					1,101,000
Issuance of preferred stock				$ 2		33,112	33,114		33,114
Issuance of preferred stock (in shares)				2,000
Surrender of restricted stock					$ (2)	(4,288)	(4,290)		(4,290)
Surrender of restricted stock (in shares)					(291,000)
Exercise of common stock options						487	487		487
Exercise of common stock options (in shares)					35,000
Amortization of equity awards						13,065	13,065		13,065
Balance (in shares) at Sep. 30, 2018				43,000	421,391,000
Adoption of accounting policy (Accounting Standards Update 2017-05 [Member]) at Dec. 31, 2017	[1]	8,098					8,098		8,098
Adoption of accounting policy (Accounting Standards Update 2016-01 [Member]) at Dec. 31, 2017	[1]	(1,136)	1,136
Balance at Dec. 31, 2017		(754,375)	(344)	$ 41	$ 4,256	6,152,764	5,402,342	127,903	5,530,245
Repurchase of common stock					$ (51)	(75,075)	(75,126)		$ (75,126)
Repurchase of common stock (in shares)					(5,100,000)				(5,100,000)
Acquisition/deconsolidation of noncontrolling interests						1,203	1,203	(48,395)	$ (47,192)
Adjustment of redeemable noncontrolling interests to estimated fair value						(3,918)	(3,918)		(3,918)
Ending balance at Sep. 30, 2018		$ (743,346)		$ 43	$ 4,214	$ 6,117,339	$ 5,378,250	$ 77,847	$ 5,456,097

[1] Represents the impact of change in accounting principles for its respective Accounting Standard Updates ("ASU"). See Footnote 2 of the Notes to Condensed Consolidated Financial Statements for additional disclosure.