SEGMENT INFORMATION - Unconsolidated Real Estate Ventures of Company's Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021
Segment Reporting Information [Line Items]
Investment in real estate ventures	$ 429,246		$ 429,246		$ 411,110
Equity in income (loss) of real estate venture	(4,981)	$ (7,240)	(9,544)	$ (14,164)
Philadelphia CBD
Segment Reporting Information [Line Items]
Investment in real estate ventures	341,748		341,748		317,959
Equity in income (loss) of real estate venture	(2,574)	(4,661)
Metropolitan Washington, D.C.
Segment Reporting Information [Line Items]
Investment in real estate ventures	85,614		85,614		85,867
Equity in income (loss) of real estate venture	(381)	(778)
Mid-Atlantic Office JV
Segment Reporting Information [Line Items]
Investment in real estate ventures	31,478		31,478		31,680
Equity in income (loss) of real estate venture	(101)	117
MAP Venture
Segment Reporting Information [Line Items]
Investment in real estate ventures	(29,594)		$ (29,594)		$ (24,396)
Equity in income (loss) of real estate venture	$ (1,925)	$ (1,918)