Disclosure about Fair Value of Financial Instruments (Carrying Amounts and Estimated Fair Values of Financial Instruments) (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Financial assets:
Equity securities	$ 15,685,000
Restricted cash	100,849,000	$ 100,753,000
Financial liabilities:
Borrowings under unsecured credit facility and commercial paper	1,587,597,000
Redeemable OP unitholder interests	121,440,000
Carrying Amount
Financial assets:
Equity securities		11,286,000
Cash and cash equivalents	284,917,000	215,376,000
Restricted cash		100,753,000
Foreign currency forward contracts, interest rate swaps and cross currency swaps	18,554,000	94,729,000
Financial liabilities:
Borrowings under unsecured credit facility and commercial paper		1,147,000,000
Senior unsecured notes	10,336,513,000	9,603,299,000
Secured debt	2,990,962,000	2,476,177,000
Foreign currency forward contracts, interest rate swaps and cross currency swaps	53,601,000	71,109,000
Redeemable OP unitholder interests	121,440,000	103,071,000
Carrying Amount | Mortgage loans receivable
Financial assets:
Loans receivable, Fair value	145,686,000	249,071,000
Carrying Amount | Other real estate loans receivable
Financial assets:
Loans receivable, Fair value	124,696,000	81,268,000
Carrying Amount | Non real estate loans receivable
Financial assets:
Loans receivable, Fair value	336,854,000	282,443,000
Fair Value
Financial assets:
Equity securities	15,685,000	11,286,000
Cash and cash equivalents	284,917,000	215,376,000
Restricted cash	100,849,000	100,753,000
Foreign currency forward contracts, interest rate swaps and cross currency swaps	18,554,000	94,729,000
Financial liabilities:
Borrowings under unsecured credit facility and commercial paper	1,587,597,000	1,147,000,000
Senior unsecured notes	11,400,571,000	10,043,797,000
Secured debt	3,041,893,000	2,499,130,000
Foreign currency forward contracts, interest rate swaps and cross currency swaps	53,601,000	71,109,000
Redeemable OP unitholder interests	121,440,000	103,071,000
Fair Value | Mortgage loans receivable
Financial assets:
Loans receivable, Fair value	150,217,000	257,337,000
Fair Value | Other real estate loans receivable
Financial assets:
Loans receivable, Fair value	128,512,000	82,742,000
Fair Value | Non real estate loans receivable
Financial assets:
Loans receivable, Fair value	$ 379,239,000	$ 384,150,000