Disclosure about Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2018		Dec. 31, 2017	Mar. 31, 2017		Dec. 31, 2016
Financial Assets:
Loans receivable, Carrying Amount	$ 436,194		$ 495,871
Loans receivable, Fair value	271,887		332,508
Available-for-sale equity investments, Carrying Amount	14,443		7,269
Available-for-sale equity investments, Fair Value	14,443		7,269
Cash And Cash Equivalents At Carrying Value	202,824		243,777	$ 423,137		$ 607,220
Cash and cash equivalents, Fair Value	202,824		243,777
Restricted cash, Carrying Value	61,295		65,526
Restricted cash, Fair Value	61,295		65,526
Foreign Currency Forward Contracts Carrying Value	28,713		15,604
Foreign Currency Forward Contracts Fair Value	28,713		15,604
Financial Liabilities:
Borrowings under primary unsecured credit facilities, Carrying Value	865,000	[1]	719,000	$ 522,000	[1]
Borrowings under primary unsecured credit facilities, Fair Value	865,000		719,000
Senior unsecured notes, Carrying Amount	7,924,340		8,331,722
Senior unsecured notes, Fair Value	8,582,136		9,168,432
Secured debt, Carrying Amount	2,488,652		2,608,976
Secured debt, Fair Value	2,465,270		2,641,997
Foreign Currency Forward Contracts Carrying Value	58,190		38,654
Foreign Currency Forward Contracts, Fair Value	58,190		38,654
Redeemable OP unitholder interests carrying value	97,476		97,476
Redeemable OP unitholder interests fair value	97,476		97,476
Mortgage Loans on Real Estate [Member]
Financial Assets:
Loans receivable, Carrying Amount	264,948		306,120
Loans receivable, Fair value	271,887		332,508
Other Real Estate Loans Receivable [Member]
Financial Assets:
Loans receivable, Carrying Amount	102,874		121,379
Loans receivable, Fair value	$ 108,850		$ 125,480

[1] As of March 31, 2018, letters of credit in the aggregate amount of $22,365,000 have been issued, which reduces the borrowing capacity on the unsecured revolving credit facility.