SEGMENT INFORMATION - Unconsolidated Real Estate Ventures of Company's Reportable Segments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
Investment in real estate ventures, at equity	$ 532,224	$ 411,110
Equity in income (loss) of real estate venture	(22,016)	(26,697)	$ (18,584)
Philadelphia CBD
Segment Reporting Information [Line Items]
Investment in real estate ventures, at equity	387,301	317,959
Equity in income (loss) of real estate venture	(11,764)	(15,191)	(9,090)
Metropolitan Washington, D.C.
Segment Reporting Information [Line Items]
Investment in real estate ventures, at equity	83,903	85,867
Equity in income (loss) of real estate venture	(2,324)	(3,755)	(3,019)
Mid-Atlantic Office Venture
Segment Reporting Information [Line Items]
Investment in real estate ventures, at equity	31,005	31,680
Equity in income (loss) of real estate venture	412	932	96
MAP Venture
Segment Reporting Information [Line Items]
Investment in real estate ventures, at equity	(35,411)	(24,396)
Equity in income (loss) of real estate venture	(8,340)	(8,683)	(6,571)
Austin, Texas
Segment Reporting Information [Line Items]
Investment in real estate ventures, at equity	65,426	0
Equity in income (loss) of real estate venture	$ 0	$ 0	$ 0