SEGMENT INFORMATION - Unconsolidated Real Estate Ventures of Company's Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Segment Reporting Information [Line Items]
Investment in real estate ventures	$ 545,491		$ 532,224
Equity in income (loss) of real estate venture	(6,167)	$ (4,563)
Philadelphia CBD
Segment Reporting Information [Line Items]
Investment in real estate ventures	404,838		387,301
Equity in income (loss) of real estate venture	(3,259)	(2,772)
Metropolitan Washington, D.C.
Segment Reporting Information [Line Items]
Investment in real estate ventures	82,281		83,903
Equity in income (loss) of real estate venture	(1,176)	(186)
Mid-Atlantic Office JV
Segment Reporting Information [Line Items]
Investment in real estate ventures	30,591		31,005
Equity in income (loss) of real estate venture	190	418
MAP Venture
Segment Reporting Information [Line Items]
Investment in real estate ventures	(38,284)		(35,411)
Equity in income (loss) of real estate venture	(1,922)	(2,023)
Austin, Texas
Segment Reporting Information [Line Items]
Investment in real estate ventures	66,065		$ 65,426
Equity in income (loss) of real estate venture	$ 0	$ 0