Disclosure about Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2017		Dec. 31, 2016	Jun. 30, 2016		Dec. 31, 2015
Financial Assets:
Loans receivable, Carrying Amount	$ 520,479		$ 622,628
Loans receivable, Fair value	405,671		521,773
Available-for-sale equity investments, Carrying Amount	11,422		27,899
Available-for-sale equity investments, Fair Value	11,422	[1]	27,899
Cash and cash equivalents, Carrying Amount	442,284		419,378	$ 466,585		$ 360,908
Cash and cash equivalents, Fair Value	442,284		419,378
Foreign Currency Forward Contracts Carrying Value	54,326		135,561
Foreign Currency Forward Contracts Fair Value	54,326		135,561
Financial Liabilities:
Borrowings under primary unsecured credit facilities, Carrying Value	385,000	[2]	645,000	$ 745,000	[2]
Borrowings under primary unsecured credit facilities, Fair Value	385,000		645,000
Senior unsecured notes, Carrying Amount	8,250,940		8,161,619
Senior unsecured notes, Fair Value	9,088,276		8,879,176
Secured debt, Carrying Amount	2,670,914		3,477,699
Secured debt, Fair Value	2,718,333		3,558,378
Foreign Currency Forward Contracts Carrying Value	10,426		4,342
Foreign Currency Forward Contracts, Fair Value	10,426		4,342
Redeemable OP unitholder interests carrying value	111,149		110,502
Redeemable OP unitholder interests fair value	111,149		110,502
Mortgage Loans on Real Estate [Member]
Financial Assets:
Loans receivable, Carrying Amount	369,141		485,735
Loans receivable, Fair value	405,671		521,773
Other Real Estate Loans Receivable [Member]
Financial Assets:
Loans receivable, Carrying Amount	151,338		136,893
Loans receivable, Fair value	$ 156,266		$ 138,050

[1] Unrealized gains or losses on equity investments are recorded in accumulated other comprehensive income (loss) at each measurement date.

[2] As of June 30, 2017, letters of credit in the aggregate amount of $32,456,000 have been issued, which reduces the borrowing capacity on the unsecured revolving credit facility.