Unconsolidated Joint Ventures (Condensed Balance Sheet Information for Joint Ventures) (Details)		3 Months Ended
	Oct. 03, 2018 USD ($) extension	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Schedule of Equity Method Investments [Line Items]
Deferred financing costs, net		$ 1,930,000	$ 2,084,000
Corporate Joint Venture
Schedule of Equity Method Investments [Line Items]
Total Assets		3,333,260,000	2,291,036,000
Total Debt		1,062,750,000	434,550,000
Total Equity		1,769,654,000	1,441,218,000
Corporate Joint Venture | Blackstone Property Partners
Schedule of Equity Method Investments [Line Items]
Debt		$ 325,000,000.0
Mortgage note interest rate		5.07%
Corporate Joint Venture | 799 Broadway Joint Venture
Schedule of Equity Method Investments [Line Items]
Amount borrowed under construction loan		$ 122,100,000
Deferred financing costs, net		$ 3,000,000.0
LIBOR (maximum)	4.00%
Extension term		1 year
Corporate Joint Venture | 799 Broadway Joint Venture | Construction loan
Schedule of Equity Method Investments [Line Items]
Maximum borrowing capacity	$ 187,000,000.0
Number of extensions available | extension	2
Corporate Joint Venture | 799 Broadway Joint Venture | LIBOR
Schedule of Equity Method Investments [Line Items]
Basis spread	4.25%
Corporate Joint Venture | Terminal Warehouse
Schedule of Equity Method Investments [Line Items]
Amount borrowed under construction loan		$ 625,500,000
Deferred financing costs, net		$ 6,700,000
Extension term		1 year
Corporate Joint Venture | Terminal Warehouse | Construction loan
Schedule of Equity Method Investments [Line Items]
Maximum borrowing capacity	$ 650,000,000.0
Corporate Joint Venture | Terminal Warehouse | LIBOR
Schedule of Equity Method Investments [Line Items]
Basis spread	3.40%
Corporate Joint Venture | Market Square Joint Venture
Schedule of Equity Method Investments [Line Items]
Total Assets		$ 579,363,000	582,747,000
Total Debt		324,828,000	324,815,000
Total Equity		242,942,000	241,719,000
Corporate Joint Venture | University Circle Joint Venture
Schedule of Equity Method Investments [Line Items]
Total Assets		217,185,000	216,546,000
Total Debt		0	0
Total Equity		211,218,000	212,656,000
Corporate Joint Venture | 333 Market Street Joint Venture
Schedule of Equity Method Investments [Line Items]
Total Assets		364,893,000	367,652,000
Total Debt		0	0
Total Equity		349,936,000	352,385,000
Corporate Joint Venture | 114 Fifth Avenue Joint Venture
Schedule of Equity Method Investments [Line Items]
Total Assets		476,785,000	485,442,000
Total Debt		0	0
Total Equity		119,831,000	127,554,000
Corporate Joint Venture | 1800 M Street Joint Venture
Schedule of Equity Method Investments [Line Items]
Total Assets		429,767,000	437,439,000
Total Debt		0	0
Total Equity		416,836,000	421,588,000
Corporate Joint Venture | 799 Broadway Joint Venture
Schedule of Equity Method Investments [Line Items]
Total Assets		220,024,000	201,210,000
Total Debt		119,156,000	109,735,000
Total Equity		88,374,000	85,316,000
Corporate Joint Venture | Terminal Warehouse
Schedule of Equity Method Investments [Line Items]
Total Assets		1,042,748,000	0
Total Debt		618,766,000	0
Total Equity		339,319,000	0
Corporate Joint Venture | Real Estate Services Joint Ventures
Schedule of Equity Method Investments [Line Items]
Total Assets		2,495,000	0
Total Debt		0	0
Total Equity		$ 1,198,000	$ 0