Investments in Unconsolidated Funds - Narrative (Details) $ in Thousands, ft² in Millions	6 Months Ended
	Jun. 30, 2020 USD ($) ft² property	Jun. 30, 2019 USD ($) ft² fund property
Schedule of Equity Method Investments [Line Items]
Number of properties	84
Acquisition of additional interests in unconsolidated Fund | $	$ 6,591	$ 7,518
Percentage of amounts related to the Fund	100.00%
Partnership X
Schedule of Equity Method Investments [Line Items]
Equity interest of the Fund (percent)	33.50%	24.60%
Purchase of additional equity interest (percent)	3.60%
Acquisition of additional interests in unconsolidated Fund | $	$ 6,600
Opportunity Fund
Schedule of Equity Method Investments [Line Items]
Equity interest of the Fund (percent)		6.20%
Fund X
Schedule of Equity Method Investments [Line Items]
Equity interest of the Fund (percent)		72.70%
Purchase of additional equity interest (percent)		1.40%
Unconsolidated Fund properties
Schedule of Equity Method Investments [Line Items]
Number of unconsolidated Funds owned and managed | fund		3
Office Buildings
Schedule of Equity Method Investments [Line Items]
Number of properties	72
Office Buildings | Unconsolidated Fund properties
Schedule of Equity Method Investments [Line Items]
Number of properties	2	8
Area of real estate portfolio (sq ft) | ft²	0.4	1.8