Acquisitions - Development Project Acquisitions and Acquisition Costs (Details) - USD ($) $ in Thousands			12 Months Ended
	Dec. 12, 2019	Aug. 19, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule of Asset Acquisitions, by Acquisition [Line Items]
Purchase price				$ 173,000
Asset acquisition, accrued liabilities				20,890
Restricted cash			$ 91,139	16,300	$ 119,430	$ 9,149
Payments to acquire land parcel				99,500
Acquisition costs, capitalized			300	1,600	$ 3,800
1335 Broadway & 901 Park Boulevard, San Diego, CA [Member]
Schedule of Asset Acquisitions, by Acquisition [Line Items]
Purchase price		$ 40,000
Asset acquisition, accrued liabilities		$ 4,000
Seattle CBD Project [Member]
Schedule of Asset Acquisitions, by Acquisition [Line Items]
Purchase price	$ 133,000
Asset acquisition, accrued liabilities				6,300
Restricted cash			$ 10,000	$ 10,000