SEGMENT INFORMATION - Net Operating Income of Company's Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Segment Reporting Information [Line Items]
Total revenue	$ 129,227	$ 127,505
Operating expenses	(50,835)	(47,918)
Net operating income	78,392	79,587
Operating Segments | Philadelphia CBD
Segment Reporting Information [Line Items]
Total revenue	56,227	53,471
Operating expenses	(20,586)	(19,743)
Net operating income	35,641	33,728
Operating Segments | Pennsylvania Suburbs
Segment Reporting Information [Line Items]
Total revenue	32,771	31,807
Operating expenses	(9,779)	(10,158)
Net operating income	22,992	21,649
Operating Segments | Austin, Texas
Segment Reporting Information [Line Items]
Total revenue	25,237	24,915
Operating expenses	(11,294)	(10,293)
Net operating income	13,943	14,622
Operating Segments | Other
Segment Reporting Information [Line Items]
Total revenue	9,389	8,799
Operating expenses	(5,412)	(5,438)
Net operating income	3,977	3,361
Corporate
Segment Reporting Information [Line Items]
Total revenue	5,603	8,513
Operating expenses	(3,764)	(2,286)
Net operating income	$ 1,839	$ 6,227