Investments In and Advances To Affiliates Consolidated Variable Interest Entity (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) ft²	Dec. 31, 2020 USD ($) ft²	Dec. 31, 2018 USD ($)
Consolidated Variable Interest Entity [Abstract]
Rentable square feet of office property under development (in sq feet) | ft²		1,200,000
Assets and liabilities of consolidated variable interest entity [Abstract]
Development in-process	$ 172,706	$ 259,681	$ 165,537
Deferred leasing costs	231,347	209,329
Prepaid expenses and other assets	58,996	62,885
Accounts payable, accrued expenses and other liabilities	$ 286,911	$ 268,727
Ownership Percentage [Member]
Consolidated Variable Interest Entity [Abstract]
Partner's interest in consolidated joint venture (in hundredths)		50.00%
Consolidated Variable Interest Entity [Member]
Consolidated Variable Interest Entity [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
Percentage of equity interest in consolidated affiliates	80.00%
Partner's contribution of property to acquire interest in consolidated joint venture	$ 5,000
Advance to consolidated affiliate	$ 46,300
Interest rate, basis spread (in hundredths)	2.50%
Amount of loan funded to affiliate		$ 18,500
Assets and liabilities of consolidated variable interest entity [Abstract]
Development in-process		46,873
Deferred leasing costs		196
Prepaid expenses and other assets		75
Accounts payable, accrued expenses and other liabilities		$ 2,693
Consolidated Variable Interest Entity [Member] | Ownership Percentage [Member]
Consolidated Variable Interest Entity [Abstract]
Partner's interest in consolidated joint venture (in hundredths)	20.00%	20.00%
London Interbank Offered Rate (LIBOR) [Member] | Consolidated Variable Interest Entity [Member]
Consolidated Variable Interest Entity [Abstract]
Interest rate basis	LIBOR