Condensed Consolidated Statements of Changes in Equity (Unaudited) - USD ($) shares in Thousands, $ 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
Balance at Dec. 31, 2014	$ (1,006,578)	$ 45,122	$ 102	$ 4,118	$ 5,732,021	$ 4,774,785	$ 126,980	$ 4,901,765
Balance (in shares) at Dec. 31, 2014			102	411,820
Contributions from noncontrolling interests							66,163	66,163
Net income	437,342					437,342	3,006	440,348
Change in unrealized gain on marketable securities		(38,547)				(38,547)		(38,547)
Change in unrealized loss on interest rate swaps		55				55		55
Change in foreign currency translation adjustment, net		(8,536)				(8,536)		(8,536)
Redeemable noncontrolling interests income							(3,045)	(3,045)
Dividends	(227,335)					(227,335)		(227,335)
Distributions to noncontrolling interests							(6,093)	(6,093)
Issuance of common stock, net (in shares)				781
Issuance of common stock, net				$ 8	480	488		488
Surrender of restricted stock (in shares)				(214)
Surrender of restricted stock				$ (2)	(5,290)	(5,292)		(5,292)
Exercise of common stock options (in shares)				732
Exercise of common stock options				$ 7	13,465	13,472		13,472
Sale of interests in investments, net of tax of $16.0 million					23,993	23,993		23,993
Acquisition of noncontrolling interests					(6,080)	(6,080)	(25,083)	(31,163)
Amortization of equity awards					9,241	9,241		9,241
Balance at Jun. 30, 2015	(796,571)	(1,906)	$ 102	$ 4,131	5,767,830	4,973,586	161,928	5,135,514
Balance (in shares) at Jun. 30, 2015			102	413,119
Balance at Dec. 31, 2015	(572,335)	5,588	$ 32	$ 4,134	5,608,881	5,046,300	135,651	5,181,951
Balance (in shares) at Dec. 31, 2015			32	413,431
Contributions from noncontrolling interests							475	475
Net income	344,122					344,122	2,878	347,000
Change in unrealized gain on marketable securities		(33)				(33)		(33)
Change in unrealized loss on interest rate swaps		(759)				(759)		(759)
Change in foreign currency translation adjustment, net		2,354				2,354		2,354
Redeemable noncontrolling interests income							(2,147)	(2,147)
Dividends	(237,135)					(237,135)		(237,135)
Distributions to noncontrolling interests							(6,299)	(6,299)
Issuance of common stock, net (in shares)				5,839
Issuance of common stock, net				$ 59	139,068	139,127		139,127
Surrender of restricted stock (in shares)				(251)
Surrender of restricted stock				$ (3)	(6,439)	(6,442)		(6,442)
Exercise of common stock options (in shares)				979
Exercise of common stock options				$ 10	17,462	17,472		17,472
Amortization of equity awards					9,121	9,121		9,121
Balance at Jun. 30, 2016	$ (465,348)	$ 7,150	$ 32	$ 4,200	$ 5,768,093	$ 5,314,127	$ 130,558	$ 5,444,685
Balance (in shares) at Jun. 30, 2016			32	419,998