Financial Instruments and Fair Value Measurements - Summary or Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Carrying value
Fair value of financial assets and liabilities
Mortgages payable assumed in connection with acquisitions	$ 285,600	$ 299,600
Notes and bonds payable	8,353,000	8,302,400
Estimated fair value
Fair value of financial assets and liabilities
Mortgages payable assumed in connection with acquisitions	297,900	309,400
Notes and bonds payable	9,000,500	9,324,000
Mortgages payable
Fair value of financial assets and liabilities
Unamortized net original issuance premiums	933	1,700
Deferred financing costs at period end	865	973
Notes and bonds payable
Fair value of financial assets and liabilities
Unamortized net original issuance premiums	7,200	14,600
Deferred financing costs at period end	$ 51,000	$ 49,200