Financial Instruments and Fair Value Measurements - Summary or Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Carrying value
Fair value of financial assets and liabilities
Mortgages payable assumed in connection with acquisitions	$ 393,700	$ 408,400
Notes and bonds payable	6,640,600	6,317,600
Estimated fair value
Fair value of financial assets and liabilities
Mortgages payable assumed in connection with acquisitions	403,800	417,700
Notes and bonds payable	7,360,000	6,826,100
Mortgages Payable
Fair value of financial assets and liabilities
Unamortized balance of non-cash net premiums	2,300	3,000
Remaining balance of deferred financing costs at period end	1,100	1,300
Notes and bonds payable
Fair value of financial assets and liabilities
Unamortized balance of non-cash net premiums	3	6,300
Remaining balance of deferred financing costs at period end	$ 38,500	$ 35,900