Disclosure about Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Financial Assets:
Loans receivable, Carrying Amount		$ 819,492	$ 380,169
Available-for-sale equity investments, Carrying Amount		22,779	0
Available-for-sale equity investments, Fair Value		22,779	0
Cash and cash equivalents, Carrying Amount		360,908	473,726	$ 158,780	$ 1,033,764
Cash and cash equivalents		360,908	473,726
Foreign Currency Forward Contracts Carrying Value		129,520	57,087
Foreign Currency Forward Contracts Fair Value		129,520	57,087
Financial Liabilities:
Borrowings under unsecured lines of credit arrangements, Carrying Amount	[1]	835,000	0	$ 130,000
Borrowings under unsecured lines of credit arrangements, Fair Value		835,000	0
Senior unsecured notes, Carrying Amount		8,548,055	7,729,405
Senior unsecured notes, Fair Value		9,020,529	8,613,702
Secured debt, Carrying Amount		3,509,142	2,963,186
Secured debt, Fair Value		3,678,564	3,053,067
Foreign Currency Forward Contracts Carrying Value		0	1,495
Foreign Currency Contracts, Liability, Fair Value Disclosure		0	1,495
Redeemable OP unitholder interests carrying value		112,029	46,722
Redeemable OP unitholder interests fair value		112,029	46,722
Mortgage Loans [Member]
Financial Assets:
Loans receivable, Carrying Amount		635,492	188,651
Loans receivable, Fair value		663,501	194,935
Other Real Estate Loans Receivable [Member]
Financial Assets:
Loans receivable, Carrying Amount		184,000	191,518
Loans receivable, Fair value		$ 185,693	$ 195,375

[1] As of December 31, 2015, letters of credit in the aggregate amount of $54,925,000 have been issued which reduce the available borrowing capacity on the primary unsecured credit facility.