SEGMENT INFORMATION - Net Operating Income of Company's Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Segment Reporting Information [Line Items]
Total revenue	$ 125,346	$ 125,882	$ 251,830	$ 255,109
Operating expenses	(46,314)	(46,019)	(93,728)	(96,854)
Net operating income	79,032	79,863	158,102	158,255
Operating Segments | Philadelphia CBD
Segment Reporting Information [Line Items]
Total revenue	56,723	56,671	112,711	112,898
Operating expenses	(19,071)	(20,257)	(38,953)	(40,843)
Net operating income	37,652	36,414	73,758	72,055
Operating Segments | Pennsylvania Suburbs
Segment Reporting Information [Line Items]
Total revenue	31,666	32,102	63,685	64,873
Operating expenses	(9,897)	(10,084)	(19,256)	(19,863)
Net operating income	21,769	22,018	44,429	45,010
Operating Segments | Austin, Texas
Segment Reporting Information [Line Items]
Total revenue	22,154	23,781	45,409	49,018
Operating expenses	(8,834)	(8,683)	(17,847)	(19,977)
Net operating income	13,320	15,098	27,562	29,041
Operating Segments | Other
Segment Reporting Information [Line Items]
Total revenue	10,308	8,888	21,276	18,277
Operating expenses	(5,132)	(4,850)	(10,594)	(10,262)
Net operating income	5,176	4,038	10,682	8,015
Corporate
Segment Reporting Information [Line Items]
Total revenue	4,495	4,440	8,749	10,043
Operating expenses	(3,380)	(2,145)	(7,078)	(5,909)
Net operating income	$ 1,115	$ 2,295	$ 1,671	$ 4,134