SEGMENT INFORMATION - Real Estate Investments, at Cost of Company's Reportable Segments (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Segment Reporting Information [Line Items]
Operating properties	$ 3,549,674	$ 3,542,232
Right of use asset - operating leases, net	18,875	19,031
Construction-in-progress	146,194	135,529
Land held for development	81,616	82,510
Prepaid leasehold interests in land held for development, net	27,762	27,762
Continuing Operations
Segment Reporting Information [Line Items]
Operating properties	3,549,674	3,542,232
Total Core Segments | Continuing Operations
Segment Reporting Information [Line Items]
Operating properties	3,241,185	3,237,096
Philadelphia CBD | Continuing Operations
Segment Reporting Information [Line Items]
Operating properties	1,535,852	1,534,893
Pennsylvania Suburbs | Continuing Operations
Segment Reporting Information [Line Items]
Operating properties	901,577	900,230
Austin, Texas | Continuing Operations
Segment Reporting Information [Line Items]
Operating properties	803,756	801,973
Other | Continuing Operations
Segment Reporting Information [Line Items]
Operating properties	$ 308,489	$ 305,136