Disclosure about Fair Value of Financial Instruments (Details) (USD $)	Mar. 31, 2015		Dec. 31, 2014	Mar. 31, 2014		Dec. 31, 2013
Financial Assets:
Loans receivable, Carrying Amount	$ 745,267,000		$ 380,169,000
Available-for-sale equity investments, Carrying Amount	46,740,000		0
Available-for-sale equity investments, Fair Value	46,740,000	[1]	0
Cash and cash equivalents, Carrying Amount	202,273,000		473,726,000	185,928,000		158,780,000
Cash and cash equivalents, Fair Value	202,273,000		473,726,000
Foreign currency forward contract, asset	73,081,000		57,087,000
Financial Liabilities:
Borrowings under primary unsecured credit facilities, Carrying Value	410,000,000	[2]	0	562,000,000	[2]
Borrowings under primary unsecured credit facilities, Fair Value	410,000,000		0
Senior unsecured notes, Carrying Amount	7,518,196,000		7,766,251,000
Senior unsecured notes, Fair Value	8,378,885,000		8,613,702,000
Secured debt, Carrying Amount	3,010,971,000		2,977,713,000
Secured debt, Fair Value	2,993,308,000		3,053,067,000
Foreign currency forward contact, liability	410,000		1,495,000
Redeemable OP unitholder interests	47,147,000		46,722,000
Mortgage Loans on Real Estate [Member]
Financial Assets:
Loans receivable, Carrying Amount	554,731,000		188,651,000
Loans receivable, Fair value	577,232,000		194,935,000
Other Real Estate Loans Receivable [Member]
Financial Assets:
Loans receivable, Carrying Amount	190,536,000		191,518,000
Loans receivable, Fair value	$ 192,005,000		$ 195,375,000

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

[2] (1) As of March 31, 2015, letters of credit in the aggregate amount of $65,335,000 have been issued, which reduces the borrowing capacity on the unsecured revolving credit facility.