SEGMENT INFORMATION - Unconsolidated Real Estate Ventures of Company's Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022
Segment Reporting Information [Line Items]
Investment in real estate ventures	$ 589,195		$ 589,195		$ 532,224
Equity in income (loss) of real estate venture	(7,598)	$ (4,981)	(13,765)	$ (9,544)
Philadelphia CBD
Segment Reporting Information [Line Items]
Investment in real estate ventures	452,365		452,365		387,301
Equity in income (loss) of real estate venture	(4,412)	(2,574)
Metropolitan Washington, D.C.
Segment Reporting Information [Line Items]
Investment in real estate ventures	82,603		82,603		83,903
Equity in income (loss) of real estate venture	(1,414)	(381)
Mid-Atlantic Office JV
Segment Reporting Information [Line Items]
Investment in real estate ventures	28,791		28,791		31,005
Equity in income (loss) of real estate venture	223	(101)
MAP Venture
Segment Reporting Information [Line Items]
Investment in real estate ventures	(41,310)		(41,310)		(35,411)
Equity in income (loss) of real estate venture	(1,995)	(1,925)
Austin, Texas
Segment Reporting Information [Line Items]
Investment in real estate ventures	66,746		$ 66,746		$ 65,426
Equity in income (loss) of real estate venture	$ 0	$ 0