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Investments in Unconsolidated Real Estate Ventures - Summary of Composition of Investments (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended	6 Months Ended
	Apr. 30, 2020	Jun. 30, 2020	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Total investments in unconsolidated real estate ventures		$ 464,437	$ 464,437		$ 543,026
Distributions of capital from unconsolidated real estate ventures			$ 70,818	$ 7,557
Prudential Global Investment Management (PGIM)
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage		50.00%	50.00%
Total investments in unconsolidated real estate ventures		$ 217,758	$ 217,758		215,624
Landmark
Schedule of Equity Method Investments [Line Items]
Total investments in unconsolidated real estate ventures		$ 70,217	$ 70,217		77,944
Landmark \| Minimum
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage		1.80%	1.80%
Landmark \| Maximum
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage		49.00%	49.00%
CBREI Venture
Schedule of Equity Method Investments [Line Items]
Total investments in unconsolidated real estate ventures		$ 66,184	$ 66,184		68,405
CBREI Venture \| Minimum
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage		5.00%	5.00%
CBREI Venture \| Maximum
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage		64.00%	64.00%
Canadian Pension Plan Investment Board (CPPIB)
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage		55.00%	55.00%
Total investments in unconsolidated real estate ventures		$ 48,164	$ 48,164		109,911
Canadian Pension Plan Investment Board (CPPIB) \| 1900 N Street
Schedule of Equity Method Investments [Line Items]
Distributions of capital from unconsolidated real estate ventures		$ 70,800
Canadian Pension Plan Investment Board (CPPIB) \| 1900 N Street \| Mortgages Payable
Schedule of Equity Method Investments [Line Items]
Maximum borrowing capacity	$ 160,000
Proceeds from loan	134,500
Remaining borrowing capacity	$ 25,500
Berkshire Group
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage		50.00%	50.00%
Total investments in unconsolidated real estate ventures		$ 47,780	$ 47,780		46,391
Brandywine
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage		30.00%	30.00%
Total investments in unconsolidated real estate ventures		$ 13,760	$ 13,760		13,830
Pacific Life Insurance Company
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage		20.00%	20.00%
Total investments in unconsolidated real estate ventures		$ 0	$ 0		10,385
Pacific Life Insurance Company \| The Marriott Wardman Park hotel
Schedule of Equity Method Investments [Line Items]
Impairment charge		6,500
Other
Schedule of Equity Method Investments [Line Items]
Total investments in unconsolidated real estate ventures		$ 574	$ 574		$ 536