Fair Value of Financial Instruments (Details) - USD ($)	Mar. 31, 2018	Dec. 31, 2017
Level 2 | Accounts payable and accrued expenses | Interest rate swaps
Fair value of financial assets and liabilities
Fair value of derivative liabilities	$ 307,000
Level 2 | Other assets, net | Interest rate swaps
Fair value of financial assets and liabilities
Fair value of derivative assets	3,600,000
Mortgages Payable
Fair value of financial assets and liabilities
Unamortized balance of non-cash net premiums	5,400,000	$ 5,900,000
Deferred financing costs	223,000	236,000
Notes and bonds payable
Fair value of financial assets and liabilities
Unamortized balance of original issuance premiums	13,900,000	14,300,000
Deferred financing costs	34,300,000	34,100,000
Carrying value
Fair value of financial assets and liabilities
Notes receivable issued in connection with property sales	5,200,000	5,300,000
Mortgages payable assumed in connection with acquisitions	308,000,000	320,300,000
Notes and bonds payable	4,900,000,000	5,250,000,000
Estimated fair value
Fair value of financial assets and liabilities
Notes receivable issued in connection with property sales	5,200,000	5,300,000
Mortgages payable assumed in connection with acquisitions	320,600,000	334,200,000
Notes and bonds payable	$ 4,974,600,000	$ 5,475,300,000