SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disaggregation of Revenue [Line Items]
Total revenue	$ 514,651	$ 506,100	$ 486,819
Corporate
Disaggregation of Revenue [Line Items]
Total revenue	19,607	23,346	18,835
Rents
Disaggregation of Revenue [Line Items]
Total revenue	479,849	470,851	451,519
Rents \| Corporate
Disaggregation of Revenue [Line Items]
Total revenue	(1,441)	(1,930)	(2,497)
Total lease revenue
Disaggregation of Revenue [Line Items]
Total revenue	469,047	453,198	433,766
Total lease revenue \| Corporate
Disaggregation of Revenue [Line Items]
Total revenue	(1,441)	(1,930)	(2,497)
Fixed rent
Disaggregation of Revenue [Line Items]
Total revenue	372,069	353,387	343,924
Fixed rent \| Corporate
Disaggregation of Revenue [Line Items]
Total revenue	(1,895)	(1,895)	(2,240)
Variable rent
Disaggregation of Revenue [Line Items]
Total revenue	96,978	99,811	89,842
Variable rent \| Corporate
Disaggregation of Revenue [Line Items]
Total revenue	454	(35)	(257)
Amortization of deferred market rents
Disaggregation of Revenue [Line Items]
Total revenue	1,291	2,582	5,377
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	9,511	15,071	12,376
Daily parking & hotel flexible stay \| Corporate
Disaggregation of Revenue [Line Items]
Total revenue	0	0	0
Third party management fees, labor reimbursement and leasing
Disaggregation of Revenue [Line Items]
Total revenue	24,417	24,132	26,444
Third party management fees, labor reimbursement and leasing \| Corporate
Disaggregation of Revenue [Line Items]
Total revenue	18,486	17,613	15,440
Other income
Disaggregation of Revenue [Line Items]
Total revenue	10,385	11,117	8,856
Other income \| Corporate
Disaggregation of Revenue [Line Items]
Total revenue	2,562	7,663	5,892
Philadelphia CBD
Disaggregation of Revenue [Line Items]
Total revenue		220,875
Philadelphia CBD \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	230,933	220,876	207,858
Philadelphia CBD \| Rents
Disaggregation of Revenue [Line Items]
Total revenue		218,078
Philadelphia CBD \| Rents \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	223,537		204,848
Philadelphia CBD \| Total lease revenue
Disaggregation of Revenue [Line Items]
Total revenue		202,380
Philadelphia CBD \| Total lease revenue \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	214,410		191,026
Philadelphia CBD \| Fixed rent
Disaggregation of Revenue [Line Items]
Total revenue		151,034
Philadelphia CBD \| Fixed rent \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	159,732		149,441
Philadelphia CBD \| Variable rent
Disaggregation of Revenue [Line Items]
Total revenue		51,346
Philadelphia CBD \| Variable rent \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	54,678		41,585
Philadelphia CBD \| Amortization of deferred market rents
Disaggregation of Revenue [Line Items]
Total revenue		1,308
Philadelphia CBD \| Amortization of deferred market rents \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	649		2,064
Philadelphia CBD \| Daily parking & hotel flexible stay
Disaggregation of Revenue [Line Items]
Total revenue		14,390
Philadelphia CBD \| Daily parking & hotel flexible stay \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	8,478		11,758
Philadelphia CBD \| Third party management fees, labor reimbursement and leasing
Disaggregation of Revenue [Line Items]
Total revenue		287
Philadelphia CBD \| Third party management fees, labor reimbursement and leasing \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	405		893
Philadelphia CBD \| Other income
Disaggregation of Revenue [Line Items]
Total revenue		2,510
Philadelphia CBD \| Other income \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	6,991		2,117
Pennsylvania Suburbs
Disaggregation of Revenue [Line Items]
Total revenue		128,940
Pennsylvania Suburbs \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	129,300	128,940	124,566
Pennsylvania Suburbs \| Rents
Disaggregation of Revenue [Line Items]
Total revenue		128,551
Pennsylvania Suburbs \| Rents \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	128,923		124,256
Pennsylvania Suburbs \| Total lease revenue
Disaggregation of Revenue [Line Items]
Total revenue		128,541
Pennsylvania Suburbs \| Total lease revenue \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	128,923		124,106
Pennsylvania Suburbs \| Fixed rent
Disaggregation of Revenue [Line Items]
Total revenue		116,926
Pennsylvania Suburbs \| Fixed rent \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	118,856		113,748
Pennsylvania Suburbs \| Variable rent
Disaggregation of Revenue [Line Items]
Total revenue		11,615
Pennsylvania Suburbs \| Variable rent \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	10,067		10,358
Pennsylvania Suburbs \| Amortization of deferred market rents
Disaggregation of Revenue [Line Items]
Total revenue		10
Pennsylvania Suburbs \| Amortization of deferred market rents \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	0		(9)
Pennsylvania Suburbs \| Daily parking & hotel flexible stay
Disaggregation of Revenue [Line Items]
Total revenue		0
Pennsylvania Suburbs \| Daily parking & hotel flexible stay \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	0		159
Pennsylvania Suburbs \| Third party management fees, labor reimbursement and leasing
Disaggregation of Revenue [Line Items]
Total revenue		35
Pennsylvania Suburbs \| Third party management fees, labor reimbursement and leasing \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	38		34
Pennsylvania Suburbs \| Other income
Disaggregation of Revenue [Line Items]
Total revenue		354
Pennsylvania Suburbs \| Other income \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	339		276
Austin, Texas
Disaggregation of Revenue [Line Items]
Total revenue		96,329
Austin, Texas \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	95,505	96,328	101,680
Austin, Texas \| Rents
Disaggregation of Revenue [Line Items]
Total revenue		95,414
Austin, Texas \| Rents \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	94,657		100,826
Austin, Texas \| Total lease revenue
Disaggregation of Revenue [Line Items]
Total revenue		93,789
Austin, Texas \| Total lease revenue \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	93,307		97,395
Austin, Texas \| Fixed rent
Disaggregation of Revenue [Line Items]
Total revenue		60,831
Austin, Texas \| Fixed rent \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	63,209		62,545
Austin, Texas \| Variable rent
Disaggregation of Revenue [Line Items]
Total revenue		32,958
Austin, Texas \| Variable rent \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	30,098		34,850
Austin, Texas \| Amortization of deferred market rents
Disaggregation of Revenue [Line Items]
Total revenue		1,264
Austin, Texas \| Amortization of deferred market rents \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	642		3,322
Austin, Texas \| Daily parking & hotel flexible stay
Disaggregation of Revenue [Line Items]
Total revenue		361
Austin, Texas \| Daily parking & hotel flexible stay \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	708		109
Austin, Texas \| Third party management fees, labor reimbursement and leasing
Disaggregation of Revenue [Line Items]
Total revenue		486
Austin, Texas \| Third party management fees, labor reimbursement and leasing \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	516		452
Austin, Texas \| Other income
Disaggregation of Revenue [Line Items]
Total revenue		429
Austin, Texas \| Other income \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	332		402
Other
Disaggregation of Revenue [Line Items]
Total revenue		36,610
Other \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	39,306		33,880
Other \| Rents
Disaggregation of Revenue [Line Items]
Total revenue		30,738
Other \| Rents \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	34,173		24,086
Other \| Total lease revenue
Disaggregation of Revenue [Line Items]
Total revenue		30,418
Other \| Total lease revenue \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	33,848		23,736
Other \| Fixed rent
Disaggregation of Revenue [Line Items]
Total revenue		26,491
Other \| Fixed rent \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	32,167		20,430
Other \| Variable rent
Disaggregation of Revenue [Line Items]
Total revenue		3,927
Other \| Variable rent \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	1,681		3,306
Other \| Amortization of deferred market rents
Disaggregation of Revenue [Line Items]
Total revenue		0
Other \| Amortization of deferred market rents \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	0		0
Other \| Daily parking & hotel flexible stay
Disaggregation of Revenue [Line Items]
Total revenue		320
Other \| Daily parking & hotel flexible stay \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	325		350
Other \| Third party management fees, labor reimbursement and leasing
Disaggregation of Revenue [Line Items]
Total revenue		5,711
Other \| Third party management fees, labor reimbursement and leasing \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	4,972		9,625
Other \| Other income
Disaggregation of Revenue [Line Items]
Total revenue		$ 161
Other \| Other income \| Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	$ 161		$ 169