Consolidated Variable Interest Entities (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2021 USD ($)	Dec. 31, 2019 USD ($) ft²	Dec. 31, 2020 USD ($)
Consolidated Variable Interest Entities [Abstract]
Total VIE assets	$ 5,754,072		$ 5,209,417
Total VIE liabilities	3,227,854		2,738,748
Assets and liabilities of consolidated variable interest entity [Abstract]
Net real estate assets	5,018,689		4,421,285
Deferred leasing costs, net	267,405		209,329
Prepaid expense and other assets, net	77,454		62,885
Accounts payable, accrued expenses and other liabilities	284,952		$ 268,727
PAC Acquisition Variable Interest Entities [Member]
Consolidated Variable Interest Entities [Abstract]
Total VIE assets	669,600
Total VIE liabilities	418,100
Total VIE cash flows from operations	5,100
Consolidated Variable Interest Entities [Member]
Consolidated Variable Interest Entities [Abstract]
Rentable square feet of office property under development (in sq feet) | ft²		150,000
Total anticipated development costs		$ 71,300
Contribution of cash to acquire interest in consolidated joint venture		$ 20,000
Interest in consolidated joint venture (in hundredths)		80.00%
Partner's contribution of property to acquire interest in consolidated joint venture		$ 5,000
Advance to consolidated affiliate		$ 46,300
Amount of loan funded to affiliate	25,900
Assets and liabilities of consolidated variable interest entity [Abstract]
Net real estate assets	52,790
Deferred leasing costs, net	1,934
Prepaid expense and other assets, net	170
Accounts payable, accrued expenses and other liabilities	$ 1,771
Consolidated Variable Interest Entities [Member] | London Interbank Offered Rate (LIBOR) [Member]
Consolidated Variable Interest Entities [Abstract]
Variable interest rate basis		LIBOR
Interest rate, basis spread (in hundredths)		2.50%
Variable Interest Entity [Member]
Consolidated Variable Interest Entities [Abstract]
Partner's interest in consolidated joint venture (in hundredths)	20.00%
Variable Interest Entity [Member] | Consolidated Variable Interest Entities [Member]
Consolidated Variable Interest Entities [Abstract]
Partner's interest in consolidated joint venture (in hundredths)		20.00%