Debt (Schedule of Debt) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Debt [Roll Forward]
Total debt, Beginning balance			$ 8,059,802
Debt Issuances, Net			2,064,531
Repayments, Extinguishment and Assumptions, Net			(3,572,937)
(Accretion) and Amortization			1,670
Total debt, Ending balance	$ 6,553,066		6,553,066
Gain on extinguishment	(2,003)	$ 0	(1,751)	$ 5,302
Note assumed by the buyer			55,000	$ 300,720
Mortgages and Other Debt [Member]
Debt [Roll Forward]
Total debt, Beginning balance			3,111,985
Debt Issuances, Net			1,423
Repayments, Extinguishment and Assumptions, Net			(238,810)
(Accretion) and Amortization			(13,388)
Total debt, Ending balance	2,861,210		2,861,210
Mortgage Notes Payable [Member]
Debt [Roll Forward]
Outstanding balance, Beginning balance			3,039,882
Net premiums (discount), Beginning balance			59,402
Deferred costs, Beginning balance			(21,020)
Debt Issuances			1,450
Debt Issuances, Deferred Costs			(27)
Repayments, Extinguishment and Assumptions			(227,503)
Repayments, Extinguishment and Assumptions, Net Premiums (Discount)			(1,364)
Repayments, Extinguishment and Assumptions, Deferred costs			510
(Accretion) and Amortization, (Premiums) Discount			(16,229)
(Accretion) and Amortization, Deferred costs			2,973
Outstanding balance, Ending balance	2,813,829		2,813,829
Net premiums (discount), Ending balance	41,809		41,809
Deferred costs, Ending balance	(17,564)		(17,564)
Notes repaid prior to maturity			83,500
Gain on extinguishment			(600)
Write off of unamortized premiums			300
Write off of prepayment penalties			900
Mortgage Notes Payable [Member] | 2016 Property Dispositions [Member]
Debt [Roll Forward]
Unamortized premium written-off			1,100
Unamortized deferred financing costs written-off			300
Other Debt [Member]
Debt [Roll Forward]
Outstanding balance, Beginning balance			33,463
Net premiums (discount), Beginning balance			258
Repayments, Extinguishment and Assumptions			(10,453)
(Accretion) and Amortization, (Premiums) Discount			(132)
Outstanding balance, Ending balance	23,010		23,010
Net premiums (discount), Ending balance	126		126
Corporate Bonds [Member]
Debt [Roll Forward]
Outstanding balance, Beginning balance			2,550,000
Net premiums (discount), Beginning balance			(2,745)
Deferred costs, Beginning balance			(10,922)
Total debt, Beginning balance			2,536,333
Debt Issuances			1,000,000
Debt Issuances, Deferred Costs			(17,128)
Debt Issuances, Net			982,872
Repayments, Extinguishment and Assumptions			(1,300,000)
Repayments, Extinguishment and Assumptions, Net Premiums (Discount)			73
Repayments, Extinguishment and Assumptions, Deferred costs			1,898
Repayments, Extinguishment and Assumptions, Net			(1,298,029)
(Accretion) and Amortization, (Premiums) Discount			565
(Accretion) and Amortization, Deferred costs			3,416
(Accretion) and Amortization			3,981
Outstanding balance, Ending balance	2,250,000		2,250,000
Net premiums (discount), Ending balance	(2,107)		(2,107)
Deferred costs, Ending balance	(22,736)		(22,736)
Total debt, Ending balance	2,225,157		2,225,157
Convertible Debt [Member]
Debt [Roll Forward]
Outstanding balance, Beginning balance			1,000,000
Net premiums (discount), Beginning balance			(17,779)
Deferred costs, Beginning balance			(19,327)
Total debt, Beginning balance			962,894
(Accretion) and Amortization, (Premiums) Discount			3,645
(Accretion) and Amortization, Deferred costs			4,152
(Accretion) and Amortization			7,797
Outstanding balance, Ending balance	1,000,000		1,000,000
Net premiums (discount), Ending balance	(14,134)		(14,134)
Deferred costs, Ending balance	(15,175)		(15,175)
Total debt, Ending balance	970,691		970,691
Credit Facility [Member]
Debt [Roll Forward]
Outstanding balance, Beginning balance			1,460,000
Deferred costs, Beginning balance			(11,410)
Total debt, Beginning balance			1,448,590
Debt Issuances			783,000
Debt Issuances, Deferred Costs			0
Debt Issuances, Net			783,000
Repayments, Extinguishment and Assumptions			(1,743,000)
Repayments, Extinguishment and Assumptions, Deferred costs			4,314
Repayments, Extinguishment and Assumptions, Net			(1,738,686)
(Accretion) and Amortization, Deferred costs			3,104
(Accretion) and Amortization			3,104
Outstanding balance, Ending balance	500,000		500,000
Deferred costs, Ending balance	(3,992)		(3,992)
Total debt, Ending balance	496,008		496,008
2016 Term Loan [Member]
Debt [Roll Forward]
Outstanding balance, Beginning balance			0
Deferred costs, Beginning balance			0
Total debt, Beginning balance			0
Debt Issuances			300,000
Debt Issuances, Deferred Costs			(2,764)
Debt Issuances, Net			297,236
Repayments, Extinguishment and Assumptions			(300,000)
Repayments, Extinguishment and Assumptions, Deferred costs			2,588
Repayments, Extinguishment and Assumptions, Net			(297,412)
(Accretion) and Amortization, Deferred costs			176
(Accretion) and Amortization			176
Outstanding balance, Ending balance	0		0
Deferred costs, Ending balance	0		0
Total debt, Ending balance	$ 0		$ 0