Mortgage Loans Payable and Unsecured Credit Facilities (Effect of Derivative Financial Instruments on Consolidated Statements of Operations and Consolidated Statements of Equity) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Designation/Cash Flow [Member] | Interest Rate Swap [Member]
Derivative Instruments Gain Loss [Line Items]
(Loss) gain recognized in other comprehensive (loss) income (effective portion)	$ (17,940,000)	$ (13,090,000)	$ 2,185,000
Continuing Operations [Member]
Derivative Instruments Gain Loss [Line Items]
Gain (loss) recognized in other comprehensive (loss) income reclassified into earnings (effective portion)	$ (6,062,000)	$ 1,196,000	$ 667,000