Condensed Consolidated Statements of Changes in Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Cumulative Distributions in Excess of Net Income	Accumulated Other Comprehensive Income	Preferred Stock	Common Stock	Paid-in Capital	Total Stockholders' Equity	Noncontrolling Interest
Balance at Dec. 31, 2013	$ 4,769,526	$ (996,058)	$ (64,982)	$ 102	$ 4,097	$ 5,689,258	$ 4,632,417	$ 137,109
Balance (in Shares) at Dec. 31, 2013				102	409,731
Contributions from noncontrolling interests	2,313							2,313
Comprehensive income:
Net income	187,810	$ 176,512					176,512	11,298
Other comprehensive income, net of tax:
Change in unrealized gain on marketable securities	$ 8,111		8,111				8,111
Change in unrealized loss on interest rate swaps
Change in foreign currency translation adjustment	$ (2,896)		$ (2,721)				(2,721)	(175)
Redeemable noncontrolling interests	(3,224)							(3,224)
Dividends	(213,989)	$ (213,989)					(213,989)
Distributions to noncontrolling interests	(24,464)							(24,464)
Issuance of common stock	11,451				$ 7	11,444	11,451
Issuance of common stock, shares					697
Surrender of restricted stock	(3,729)				$ (2)	(3,727)	(3,729)
Surrender of restricted stock,shares					(175)
Exercise of common stock options	12,336				$ 8	12,328	12,336
Exercise of common stock options ,shares					766
Sale of interests in investments, net of tax of $16 million
Acquisition of noncontrolling interests	(819)					(53)	(53)	(766)
Amortization of equity awards	6,293					6,293	6,293
Balance at Jun. 30, 2014	4,748,719	$ (1,033,535)	$ (59,592)	$ 102	$ 4,110	5,715,543	4,626,628	122,091
Balance (in Shares) at Jun. 30, 2014				102	411,019
Balance at Dec. 31, 2014	4,901,765	$ (1,006,578)	45,122	$ 102	$ 4,118	5,732,021	4,774,785	126,980
Balance (in Shares) at Dec. 31, 2014				102	411,820
Contributions from noncontrolling interests	66,163							66,163
Comprehensive income:
Net income	440,348	$ 437,342					437,342	3,006
Other comprehensive income, net of tax:
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	(8,536)		$ (8,536)				(8,536)
Redeemable noncontrolling interests	(3,045)							(3,045)
Dividends	(227,335)	$ (227,335)					(227,335)
Distributions to noncontrolling interests	(6,093)							(6,093)
Issuance of common stock	488				$ 8	480	488
Issuance of common stock, shares					781
Surrender of restricted stock	(5,292)				$ (2)	(5,290)	(5,292)
Surrender of restricted stock,shares					(214)
Exercise of common stock options	13,472				$ 7	13,465	13,472
Exercise of common stock options ,shares					732
Sale of interests in investments, net of tax of $16 million	23,993					23,993	23,993
Acquisition of noncontrolling interests	(31,163)					(6,080)	(6,080)	(25,083)
Amortization of equity awards	9,241					9,241	9,241
Balance at Jun. 30, 2015	$ 5,135,514	$ (796,571)	$ (1,906)	$ 102	$ 4,131	$ 5,767,830	$ 4,973,586	$ 161,928
Balance (in Shares) at Jun. 30, 2015				102	413,119