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	514,914					514,914	6,518	521,432
Change in unrealized gain on marketable securities		(44,418)				(44,418)		(44,418)
Change in unrealized loss on interest rate swaps		(475)				(475)		(475)
Change in foreign currency translation adjustment, net		(14,973)				(14,973)		(14,973)
Redeemable noncontrolling interests income							(5,822)	(5,822)
Dividends	(341,082)					(341,082)		(341,082)
Distributions to noncontrolling interests							(6,706)	(6,706)
Issuance of common stock, net (in shares)				784
Issuance of common stock, net				$ 8	480	488		488
Surrender of restricted stock (in shares)				(227)
Surrender of restricted stock				$ (2)	(5,602)	(5,604)		(5,604)
Exercise of common stock options (in shares)				846
Exercise of common stock options				$ 8	15,559	15,567		15,567
Sale of interests in investments, net of tax of $16.0 million					23,993	23,993		23,993
Acquisition of noncontrolling interests					(6,437)	(6,437)	(25,189)	(31,626)
Amortization of equity awards					10,956	10,956		10,956
Balance at Sep. 30, 2015	(832,746)	(14,744)	$ 102	$ 4,132	5,770,970	4,927,714	161,944	5,089,658
Balance (in shares) at Sep. 30, 2015			102	413,223
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							507	507
Net income	300,577					300,577	4,875	305,452
Change in unrealized gain on marketable securities		18				18		18
Change in unrealized loss on interest rate swaps		(432)				(432)		(432)
Change in foreign currency translation adjustment, net		971				971		971
Redeemable noncontrolling interests income							(3,240)	(3,240)
Dividends	(357,068)					(357,068)		(357,068)
Distributions to noncontrolling interests							(7,288)	(7,288)
Issuance of common stock, net (in shares)				10,701
Issuance of common stock, net				$ 107	285,757	285,864		285,864
Surrender of restricted stock (in shares)				(270)
Surrender of restricted stock				$ (3)	(6,901)	(6,904)		(6,904)
Exercise of common stock options (in shares)				1,151
Exercise of common stock options				$ 12	20,732	20,744		20,744
Amortization of equity awards					11,387	11,387		11,387
Balance at Sep. 30, 2016	$ (628,826)	$ 6,145	$ 32	$ 4,250	$ 5,919,856	$ 5,301,457	$ 130,505	$ 5,431,962
Balance (in shares) at Sep. 30, 2016			32	425,013