SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Disaggregation of Revenue [Line Items]
Total revenue	$ 505,517	$ 514,651	$ 506,100
Corporate
Disaggregation of Revenue [Line Items]
Total revenue	25,174	19,607	23,346
Rents
Disaggregation of Revenue [Line Items]
Total revenue	469,242	479,849	470,851
Rents | Corporate
Disaggregation of Revenue [Line Items]
Total revenue	(1,772)	(1,441)	(1,930)
Total lease revenue
Disaggregation of Revenue [Line Items]
Total revenue	458,287	469,047	453,198
Total lease revenue | Corporate
Disaggregation of Revenue [Line Items]
Total revenue	(1,773)	(1,441)	(1,930)
Fixed rent
Disaggregation of Revenue [Line Items]
Total revenue	363,839	372,069	353,387
Fixed rent | Corporate
Disaggregation of Revenue [Line Items]
Total revenue	(1,631)	(1,895)	(1,895)
Variable rent
Disaggregation of Revenue [Line Items]
Total revenue	94,448	96,978	99,811
Variable rent | Corporate
Disaggregation of Revenue [Line Items]
Total revenue	(142)	454	(35)
Amortization of deferred market rents
Disaggregation of Revenue [Line Items]
Total revenue	919	1,291	2,582
Amortization of deferred market rents | Corporate
Disaggregation of Revenue [Line Items]
Total revenue	0	0	0
Daily parking & hotel flexible stay
Disaggregation of Revenue [Line Items]
Total revenue	10,036	9,511	15,071
Daily parking & hotel flexible stay | Corporate
Disaggregation of Revenue [Line Items]
Total revenue	1	0	0
Third party management fees, labor reimbursement and leasing
Disaggregation of Revenue [Line Items]
Total revenue	23,742	24,417	24,132
Third party management fees, labor reimbursement and leasing | Corporate
Disaggregation of Revenue [Line Items]
Total revenue	19,191	18,486	17,613
Other income
Disaggregation of Revenue [Line Items]
Total revenue	12,533	10,385	11,117
Other income | Corporate
Disaggregation of Revenue [Line Items]
Total revenue	7,755	2,562	7,663
Philadelphia CBD | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	225,986	230,933	220,875
Philadelphia CBD | Rents | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	222,020	223,537	218,078
Philadelphia CBD | Total lease revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	212,646	214,410	202,380
Philadelphia CBD | Fixed rent | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	158,382	159,732	151,034
Philadelphia CBD | Variable rent | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	54,264	54,678	51,346
Philadelphia CBD | Amortization of deferred market rents | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	647	649	1,308
Philadelphia CBD | Daily parking & hotel flexible stay | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	8,727	8,478	14,390
Philadelphia CBD | Third party management fees, labor reimbursement and leasing | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	158	405	287
Philadelphia CBD | Other income | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	3,808	6,991	2,510
Pennsylvania Suburbs | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	125,011	129,300	128,940
Pennsylvania Suburbs | Rents | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	124,516	128,923	128,551
Pennsylvania Suburbs | Total lease revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	124,516	128,923	128,541
Pennsylvania Suburbs | Fixed rent | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	114,056	118,856	116,926
Pennsylvania Suburbs | Variable rent | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	10,460	10,067	11,615
Pennsylvania Suburbs | Amortization of deferred market rents | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	0	0	10
Pennsylvania Suburbs | Daily parking & hotel flexible stay | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	0	0	0
Pennsylvania Suburbs | Third party management fees, labor reimbursement and leasing | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	21	38	35
Pennsylvania Suburbs | Other income | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	474	339	354
Austin, Texas | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	87,208	95,505	96,329
Austin, Texas | Rents | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	86,272	94,657	95,414
Austin, Texas | Total lease revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	85,044	93,307	93,789
Austin, Texas | Fixed rent | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	56,620	63,209	60,831
Austin, Texas | Variable rent | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	28,424	30,098	32,958
Austin, Texas | Amortization of deferred market rents | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	272	642	1,264
Austin, Texas | Daily parking & hotel flexible stay | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	956	708	361
Austin, Texas | Third party management fees, labor reimbursement and leasing | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	603	516	486
Austin, Texas | Other income | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	333	332	429
Other | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	42,138	39,306	36,610
Other | Rents | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	38,206	34,173	30,738
Other | Total lease revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	37,854	33,848	30,418
Other | Fixed rent | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	36,412	32,167	26,491
Other | Variable rent | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	1,442	1,681	3,927
Other | Amortization of deferred market rents | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	0	0	0
Other | Daily parking & hotel flexible stay | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	352	325	320
Other | Third party management fees, labor reimbursement and leasing | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	3,769	4,972	5,711
Other | Other income | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	$ 163	$ 161	$ 161