Disclosure about Fair Value of Financial Instruments - Carrying Amounts and Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Financial assets:
Equity securities	$ 10,617
Restricted cash	64,947	$ 100,753	[1]
Financial liabilities:
Unsecured revolving credit facility and commercial paper note program	1,334,586
Carrying Amount
Financial assets:
Equity securities	10,617	11,286
Cash and cash equivalents	265,788	215,376
Restricted cash	64,947	100,753
Foreign currency forward contracts, interest rate swaps and cross currency swaps	153,179	94,729
Financial liabilities:
Unsecured revolving credit facility and commercial paper note program		1,147,000
Senior unsecured notes	9,730,047	9,603,299
Secured debt	2,623,010	2,476,177
Foreign currency forward contracts, interest rate swaps and cross currency swaps	59,120	71,109
Redeemable OP unitholder interests	134,610	103,071
Carrying Amount | Mortgage loans receivable
Financial assets:
Loans receivable	252,617	249,071
Carrying Amount | Other real estate loans receivable
Financial assets:
Loans receivable	108,913	81,268
Fair Value
Financial assets:
Equity securities	10,617	11,286
Cash and cash equivalents	265,788	215,376
Restricted cash	64,947	100,753
Foreign currency forward contracts, interest rate swaps and cross currency swaps	153,179	94,729
Financial liabilities:
Unsecured revolving credit facility and commercial paper note program	1,334,586	1,147,000
Senior unsecured notes	10,229,289	10,043,797
Secured debt	2,688,384	2,499,130
Foreign currency forward contracts, interest rate swaps and cross currency swaps	59,120	71,109
Redeemable OP unitholder interests	134,610	103,071
Fair Value | Mortgage loans receivable
Financial assets:
Loans receivable	257,060	257,337
Fair Value | Other real estate loans receivable
Financial assets:
Loans receivable	$ 109,400	$ 82,742

[1] The consolidated balance sheet at December 31, 2018 has been derived from the audited financial statements at that date but does not include all of the information and footnotes required by U.S. generally accepted accounting principles for complete financial statements.