Prepaid Expenses and Other Assets, net (Details) - USD ($)		3 Months Ended
	Sep. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Variable Interest Entity [Line Items]
Deposits for future acquisitions	$ 20,500,000		$ 0
Goodwill	8,754,000		8,754,000
Non-real estate investments	5,545,000		2,713,000
Derivative assets	655,000		16,687,000
Other	33,698,000		27,479,000
Prepaid expenses and other assets, net	69,152,000		$ 55,633,000
Unrealized gain on observable changes in fair value	928,000
Washington State Convention Center Addition
Variable Interest Entity [Line Items]
Deposits for future acquisitions		$ 20,500,000
Purchase price of assets acquired		$ 86,000,000.0
Remaining future commitment expected to be settled	65,500,000
Real Estate Technology Venture Capital Fund
Variable Interest Entity [Line Items]
Commitment to fund real estate technology venture capital fund	20,000,000.0
Contributions to date	2,800,000
Remaining contribution amount	$ 17,200,000