SEGMENT INFORMATION - Real Estate Investments, at Cost of Company's Reportable Segments (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Segment Reporting Information [Line Items]
Operating properties	$ 3,597,211	$ 3,617,240
Right of use asset - operating leases, net	19,346	19,664
Construction-in-progress	245,677	218,869
Land held for development	71,493	76,499
Prepaid leasehold interests in land held for development, net	27,762	35,576
Discontinued Operations
Segment Reporting Information [Line Items]
Operating properties	52,664	0
Continuing Operations
Segment Reporting Information [Line Items]
Operating properties	3,649,875	3,617,240
Total Core Segments
Segment Reporting Information [Line Items]
Operating properties	3,224,429	3,248,182
Philadelphia CBD
Segment Reporting Information [Line Items]
Operating properties	1,519,616	1,517,801
Pennsylvania Suburbs
Segment Reporting Information [Line Items]
Operating properties	906,584	878,546
Austin, Texas
Segment Reporting Information [Line Items]
Operating properties	798,229	851,835
Other
Segment Reporting Information [Line Items]
Operating properties	$ 372,782	$ 369,058