Disclosure about Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Financial Assets:
Loans receivable, Carrying Amount		$ 622,628	$ 819,492
Available-for-sale equity investments, Carrying Amount		27,899	22,779
Available-for-sale equity investments, Fair Value		27,899	22,779
Cash and cash equivalents, Carrying Amount		419,378	360,908	$ 473,726	$ 158,780
Cash and cash equivalents, Fair Value		419,378	360,908
Foreign Currency Forward Contracts Carrying Value		135,561	129,520
Foreign Currency Forward Contracts Fair Value		135,561	129,520
Financial Liabilities:
Borrowings under unsecured lines of credit arrangements, Carrying Amount	[1]	645,000	835,000	$ 0
Borrowings under unsecured lines of credit arrangements, Fair Value		645,000	835,000
Senior unsecured notes, Carrying Amount		8,161,619	8,548,055
Senior unsecured notes, Fair Value		8,879,176	9,020,529
Secured debt, Carrying Amount		3,477,699	3,509,142
Secured debt, Fair Value		3,558,378	3,678,564
Foreign Currency Forward Contracts Carrying Value		4,342	0
Foreign Currency Contracts, Liability, Fair Value Disclosure		4,342	0
Redeemable OP unitholder interests carrying value		110,502	112,029
Redeemable OP unitholder interests fair value		110,502	112,029
Mortgage Loans [Member]
Financial Assets:
Loans receivable, Carrying Amount		485,735	635,492
Loans receivable, Fair value		521,773	663,501
Other Real Estate Loans Receivable [Member]
Financial Assets:
Loans receivable, Carrying Amount		136,893	184,000
Loans receivable, Fair value		$ 138,050	$ 185,693

[1] As of December 31, 2016, letters of credit in the aggregate amount of $41,878,000 have been issued, which reduces the available borrowing capacity on the primary unsecured revolving credit facility.