Fair Value of Financial Instruments (Details) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Level 2 | Accounts payable and accrued expenses | Interest rate swaps
Fair value of financial assets and liabilities
Fair value of derivative liabilities	$ 871,000
Level 2 | Other assets, net | Interest rate swaps
Fair value of financial assets and liabilities
Fair value of derivative assets	73,000
Mortgages Payable
Fair value of financial assets and liabilities
Unamortized balance of non-cash net premiums	4,800,000	$ 6,400,000
Remaining balance of deferred financing costs at period end	249,000	324,000
Notes and bonds payable
Fair value of financial assets and liabilities
Unamortized balance of original issuance discounts	7,100,000	19,800,000
Remaining balance of deferred financing costs at period end	24,200,000	20,800,000
Carrying value per balance sheet
Fair value of financial assets and liabilities
Notes receivable issued in connection with property sales	5,300,000	5,400,000
Mortgages payable assumed in connection with acquisitions	336,500,000	460,000,000
Notes and bonds payable	4,500,000,000	3,975,000,000
Estimated fair value
Fair value of financial assets and liabilities
Notes receivable issued in connection with property sales	5,400,000	5,500,000
Mortgages payable assumed in connection with acquisitions	351,000,000	468,700,000
Notes and bonds payable	$ 4,714,700,000	$ 4,143,300,000