Debt (Schedule of Debt) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2016 USD ($)
Debt [Roll Forward]
Deferred costs, Beginning balance	$ (26,110)
Total debt, Beginning balance	8,059,802
Debt Issuances	203,206
Repayments, Extinguishment and Assumptions	(460,715)
Accretion and (Amortization)	272
Deferred costs, Ending balance	(23,499)
Total debt, Ending balance	7,802,565
Mortgages and Other Debt [Member]
Debt [Roll Forward]
Total debt, Beginning balance	3,111,985
Debt Issuances	206
Repayments, Extinguishment and Assumptions	(77,715)
Accretion and (Amortization)	(4,810)
Total debt, Ending balance	3,029,666
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	206
Repayments, Extinguishment and Assumptions	(72,785)
Repayments, Extinguishment and Assumptions, Net Premiums	(1,096)
Repayments, Extinguishment and Assumptions, Deferred costs	329
Accretion and (Amortization), (Premiums) Discount	(5,777)
Accretion and (Amortization), Deferred costs	1,017
Outstanding balance, Ending balance	2,967,303
Net premiums (discount), Ending balance	52,529
Deferred costs, Ending balance	(19,674)
Total debt, Ending balance	2,967,303
Other Debt [Member]
Debt [Roll Forward]
Outstanding balance, Beginning balance	33,463
Net premiums (discount), Beginning balance	258
Repayments, Extinguishment and Assumptions	(4,163)
Accretion and (Amortization), (Premiums) Discount	(50)
Outstanding balance, Ending balance	29,300
Net premiums (discount), Ending balance	208
Total debt, Ending balance	29,300
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
Accretion and (Amortization), (Premiums) Discount	197
Accretion and (Amortization), Deferred costs	1,169
Accretion and (Amortization)	1,366
Outstanding balance, Ending balance	2,550,000
Net premiums (discount), Ending balance	(2,548)
Deferred costs, Ending balance	(9,753)
Total debt, Ending balance	2,537,699
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	1,201
Accretion and (Amortization), Deferred costs	1,374
Accretion and (Amortization)	2,575
Outstanding balance, Ending balance	1,000,000
Net premiums (discount), Ending balance	(16,578)
Deferred costs, Ending balance	(17,953)
Total debt, Ending balance	965,469
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	203,000
Repayments, Extinguishment and Assumptions	(383,000)
Accretion and (Amortization), Deferred costs	1,141
Accretion and (Amortization)	1,141
Outstanding balance, Ending balance	1,280,000
Deferred costs, Ending balance	(10,269)
Total debt, Ending balance	$ 1,269,731