Investments In and Advances To Affiliates Consolidated Variable Interest Entity (Details) $ in Thousands	3 Months Ended
	Jun. 30, 2019 USD ($) ft²	Dec. 31, 2019 USD ($) ft²	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Consolidated Variable Interest Entity [Abstract]
Rentable square feet of office property under development (in sq feet) | ft²		1,200,000
Partner's interest in consolidated joint venture (in hundredths)		50.00%
Assets and liabilities of consolidated variable interest entity [Abstract]
Development in-process		$ 172,706	$ 165,537	$ 88,452
Accounts payable, accrued expenses and other liabilities		286,911	$ 218,922
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
Contributions funded to acquire interest in consolidated joint venture		15,900
Percentage of equity interest in consolidated affiliates	80.00%
Partner's contribution of property to acquire interest in consolidated joint venture	$ 5,000
Partner's interest in consolidated joint venture (in hundredths)	20.00%
Advance to consolidated affiliate	$ 46,300
Assets and liabilities of consolidated variable interest entity [Abstract]
Development in-process		22,380
Accounts payable, accrued expenses and other liabilities		$ 1,162
London Interbank Offered Rate (LIBOR) [Member] | Consolidated Variable Interest Entity [Member]
Consolidated Variable Interest Entity [Abstract]
Interest rate basis	LIBOR plus 250 basis points
Interest rate, basis spread (in hundredths)	2.50%