SEGMENT INFORMATION - Net Operating Income of Company's Reportable Segments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Segment Reporting Information [Line Items]
Total revenue	$ 505,517	$ 514,651	$ 506,100
Operating expenses	(187,330)	(189,947)	(194,401)
Net operating income	318,187	324,704	311,699
Operating Segments | Philadelphia CBD
Segment Reporting Information [Line Items]
Total revenue	225,986	230,933	220,875
Operating expenses	(81,061)	(79,579)	(79,827)
Net operating income	144,925	151,354	141,048
Operating Segments | Pennsylvania Suburbs
Segment Reporting Information [Line Items]
Total revenue	125,011	129,300	128,940
Operating expenses	(38,822)	(39,584)	(41,814)
Net operating income	86,189	89,716	87,126
Operating Segments | Austin, Texas
Segment Reporting Information [Line Items]
Total revenue	87,208	95,505	96,329
Operating expenses	(34,033)	(38,453)	(41,141)
Net operating income	53,175	57,052	55,188
Operating Segments | Other
Segment Reporting Information [Line Items]
Total revenue	42,139	39,306	36,610
Operating expenses	(20,698)	(21,134)	(21,165)
Net operating income	21,441	18,172	15,445
Corporate
Segment Reporting Information [Line Items]
Total revenue	25,173	19,607	23,346
Operating expenses	(12,716)	(11,197)	(10,454)
Net operating income	$ 12,457	$ 8,410	$ 12,892