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
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	310,342					310,342	2,397	312,739
Change in unrealized gain on marketable securities		15,718				15,718		15,718
Change in unrealized loss on interest rate swaps		(352)				(352)		(352)
Change in foreign currency translation adjustment, net		(9,532)				(9,532)		(9,532)
Redeemable noncontrolling interests income							(1,522)	(1,522)
Dividends	(113,613)					(113,613)		(113,613)
Distributions to noncontrolling interests							(260)	(260)
Issuance of common stock (in shares)				539
Issuance of common stock				$ 5	481	486		486
Surrender of restricted stock (in shares)				(204)
Surrender of restricted stock				$ (2)	(5,170)	(5,172)		(5,172)
Exercise of common stock options (in shares)				554
Exercise of common stock options				$ 6	10,252	10,258		10,258
Sale of interests in investments, net of tax of $16.0 million					23,336	23,336		23,336
Amortization of equity awards					6,918	6,918		6,918
Balance at Mar. 31, 2015	(809,849)	50,956	$ 102	$ 4,127	5,767,838	5,013,174	193,758	5,206,932
Balance (in shares) at Mar. 31, 2015			102	412,709
Exercise of common stock options				$ (6)	(10,252)	(10,258)		(10,258)
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
Net income	140,713					140,713	1,441	142,154
Change in unrealized gain on marketable securities		2				2		2
Change in unrealized loss on interest rate swaps		(604)				(604)		(604)
Change in foreign currency translation adjustment, net		2,510				2,510		2,510
Redeemable noncontrolling interests income							(1,078)	(1,078)
Dividends	(118,481)					(118,481)		(118,481)
Distributions to noncontrolling interests							(1,276)	(1,276)
Issuance of common stock (in shares)				4,487
Issuance of common stock				$ 45	100,911	100,956		100,956
Surrender of restricted stock (in shares)				(228)
Surrender of restricted stock				$ (2)	(5,906)	(5,908)		(5,908)
Exercise of common stock options (in shares)				592
Exercise of common stock options				$ (6)	(10,539)	(10,545)		(10,545)
Amortization of equity awards					6,586	6,586		6,586
Balance at Mar. 31, 2016	$ (550,103)	$ 7,496	$ 32	$ 4,183	5,721,011	5,182,619	$ 134,738	5,317,357
Balance (in shares) at Mar. 31, 2016			32	418,282
Exercise of common stock options				$ 6	$ 10,539	$ 10,545		$ 10,545