Disclosure about Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Financial Assets:
Loans receivable, Carrying Amount	$ 409,196	$ 495,871
Equity securities, carrying amount	12,912	7,269
Equity securities, fair value disclosure	12,912	7,269
Cash and Cash Equivalents, at Carrying Value	191,199	243,777
Cash and cash equivalents, Fair Value	191,199	243,777
Restricted cash, carrying amount	90,086	65,526
Restricted Cash, Fair Value Disclosure	90,086	65,526
Foreign Currency Forward Contracts Carrying Value	34,902	15,604
Foreign Currency Forward Contracts Fair Value	34,902	15,604
Financial Liabilities:
Borrowings under primary unsecured credit facility, Carrying Value	1,312,000	719,000	$ 420,000
Borrowings under primary unsecured credit facilities, Fair Value	1,312,000	719,000
Senior unsecured notes, Carrying Amount	9,655,022	8,331,722
Senior unsecured notes, Fair Value	10,169,806	9,168,432
Secured debt, Carrying Amount	2,465,661	2,608,976
Secured debt, Fair Value	2,464,635	2,641,997
Foreign Currency Forward Contracts Carrying Value	78,566	38,654
Foreign Currency Forward Contracts, Fair Value	78,566	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
Financial Assets:
Loans receivable, Carrying Amount	266,286	306,120
Loans receivable, Fair value	273,620	332,508
Other Real Estate Loans Receivable
Financial Assets:
Loans receivable, Carrying Amount	74,538	121,379
Loans receivable, Fair value	$ 75,091	$ 125,480