SEGMENT INFORMATION - Unconsolidated Real Estate Ventures of Company's Reportable Segments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Segment Reporting Information [Line Items]
Investment in real estate ventures, at equity	$ 552,494	$ 532,224
Equity in income (loss) of real estate venture	(77,915)	(22,016)	$ (26,697)
Philadelphia CBD
Segment Reporting Information [Line Items]
Investment in real estate ventures, at equity	450,136	387,301
Equity in income (loss) of real estate venture	(25,793)	(11,764)	(15,191)
Mid-Atlantic Office JV
Segment Reporting Information [Line Items]
Investment in real estate ventures, at equity	0	31,005
Equity in income (loss) of real estate venture	(26,448)	412	932
MAP Venture
Segment Reporting Information [Line Items]
Investment in real estate ventures, at equity	(48,733)	(35,411)
Equity in income (loss) of real estate venture	(10,581)	(8,340)	(8,683)
Austin, Texas
Segment Reporting Information [Line Items]
Investment in real estate ventures, at equity	79,160	65,426
Equity in income (loss) of real estate venture	0	0	0
Other
Segment Reporting Information [Line Items]
Investment in real estate ventures, at equity	71,931	83,903
Equity in income (loss) of real estate venture	$ (15,093)	$ (2,324)	$ (3,755)