SEGMENT INFORMATION - Unconsolidated Real Estate Ventures of Company's Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Segment Reporting Information [Line Items]
Investment in real estate ventures	$ 592,948		$ 592,948		$ 532,224
Equity in income (loss) of real estate venture	(10,739)	$ (6,260)	(24,504)	$ (15,804)
Philadelphia CBD
Segment Reporting Information [Line Items]
Investment in real estate ventures	453,917		453,917		387,301
Equity in income (loss) of real estate venture	(6,537)	(3,452)	(14,208)	(8,798)
Metropolitan Washington, D.C.
Segment Reporting Information [Line Items]
Investment in real estate ventures	82,350		82,350		83,903
Equity in income (loss) of real estate venture	(1,306)	(706)	(3,896)	(1,273)
Mid-Atlantic Office JV
Segment Reporting Information [Line Items]
Investment in real estate ventures	28,335		28,335		31,005
Equity in income (loss) of real estate venture	182	(83)	595	234
MAP Venture
Segment Reporting Information [Line Items]
Investment in real estate ventures	(45,148)		(45,148)		(35,411)
Equity in income (loss) of real estate venture	(3,078)	(2,019)	(6,995)	(5,967)
Austin, Texas
Segment Reporting Information [Line Items]
Investment in real estate ventures	73,494		73,494		$ 65,426
Equity in income (loss) of real estate venture	$ 0	$ 0	$ 0	$ 0