Disclosure about Fair Value of Financial Instruments (Details)	Sep. 30, 2014 USD ($)		Sep. 30, 2014 CAD	Sep. 30, 2014 GBP (£)	Dec. 31, 2013 USD ($)	Sep. 30, 2013 USD ($)	Dec. 31, 2012 USD ($)	Sep. 30, 2014 Mortgage Loans on Real Estate [Member] USD ($)	Dec. 31, 2013 Mortgage Loans on Real Estate [Member] USD ($)	Sep. 30, 2014 Other Real Estate Loans Receivable [Member] USD ($)	Dec. 31, 2013 Other Real Estate Loans Receivable [Member] USD ($)
Financial Assets:
Loans receivable, Carrying Amount	$ 318,221,000				$ 332,146,000			$ 102,241,000	$ 146,987,000	$ 215,980,000	$ 185,159,000
Loans receivable, Fair value								104,786,000	148,088,000	217,952,000	188,920,000
Available-for-sale equity investments, Carrying Amount					1,211,000
Available-for-sale equity investments, Fair Value					1,211,000
Cash and cash equivalents, Carrying Amount	998,678,000				158,780,000	164,838,000	1,033,764,000
Cash and cash equivalents, Fair Value	998,678,000				158,780,000
Foreign currency forward contract, asset	46,183,000
Interest rate derivative, Fair Value, Asset	1,000	[1]			38,000
Financial Liabilities:
Borrowings under primary unsecured credit facilities, Carrying Value	0		0	0	130,000,000	847,670,000
Borrowings under primary unsecured credit facilities, Fair Value					130,000,000
Senior unsecured notes, Carrying Amount	7,305,414,000				7,379,308,000
Senior unsecured notes, Fair Value	8,034,352,000				7,743,730,000
Secured debt, Carrying Amount	2,893,814,000				3,058,248,000
Secured debt, Fair Value	2,953,223,000				3,168,775,000
Foreign currency forward contact, liability	14,756,000				11,637,000
Redeemable OP unitholder interests	$ 39,987,000

[1] (1) Please see Note 11 for additional information.