SCHEDULE III REAL ESTATE AND ACCUMULATED DEPRECIATION (Details) - USD ($)	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
REAL ESTATE AND ACCUMULATED DEPRECIATION
Encumbrances	$ 0
Accumulated Depreciation	366,349,000	$ 423,417,000	$ 424,487,000	$ 538,717,000
Aggregate cost for Federal Income Tax purposes	1,401,985
Real Estate Excluding Assets Held For Sale
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	110,889,000
Initial cost of Buildings Improvements and Equipment	865,439,000
Costs Capitalized (Disposals) Subsequent to Acquisition	280,845,000
Historical Cost of Land	110,298,000
Historical Cost of Buildings Improvements and Equipment	1,146,875,000
Total	1,257,173,000
Accumulated Depreciation	366,349,000
Total Costs, Net of Accumulated Depreciation	890,824,000
Park Ten, Houston, TX
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	1,061,000
Initial cost of Buildings Improvements and Equipment	21,303,000
Costs Capitalized (Disposals) Subsequent to Acquisition	8,100,000
Historical Cost of Land	565,000
Historical Cost of Buildings Improvements and Equipment	29,899,000
Total	30,464,000
Accumulated Depreciation	15,649,000
Total Costs, Net of Accumulated Depreciation	$ 14,815,000
Park Ten, Houston, TX | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
Park Ten, Houston, TX | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
Addison, Addison, TX
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 4,325,000
Initial cost of Buildings Improvements and Equipment	48,040,000
Costs Capitalized (Disposals) Subsequent to Acquisition	13,860,000
Historical Cost of Land	4,325,000
Historical Cost of Buildings Improvements and Equipment	61,900,000
Total	66,225,000
Accumulated Depreciation	30,173,000
Total Costs, Net of Accumulated Depreciation	$ 36,052,000
Addison, Addison, TX | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
Addison, Addison, TX | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
Greenwood, Englewood, CO
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 3,100,000
Initial cost of Buildings Improvements and Equipment	30,201,000
Costs Capitalized (Disposals) Subsequent to Acquisition	11,584,000
Historical Cost of Land	3,100,000
Historical Cost of Buildings Improvements and Equipment	41,785,000
Total	44,885,000
Accumulated Depreciation	20,108,000
Total Costs, Net of Accumulated Depreciation	$ 24,777,000
Greenwood, Englewood, CO | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
Greenwood, Englewood, CO | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
Innsbrook, Glenn Allen, VA
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 5,000,000
Initial cost of Buildings Improvements and Equipment	40,216,000
Costs Capitalized (Disposals) Subsequent to Acquisition	14,199,000
Historical Cost of Land	5,000,000
Historical Cost of Buildings Improvements and Equipment	54,415,000
Total	59,415,000
Accumulated Depreciation	21,809,000
Total Costs, Net of Accumulated Depreciation	$ 37,606,000
Innsbrook, Glenn Allen, VA | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
Innsbrook, Glenn Allen, VA | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
Eldridge Green, Houston, TX
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 3,900,000
Initial cost of Buildings Improvements and Equipment	43,791,000
Costs Capitalized (Disposals) Subsequent to Acquisition	12,400,000
Historical Cost of Land	3,900,000
Historical Cost of Buildings Improvements and Equipment	56,191,000
Total	60,091,000
Accumulated Depreciation	23,906,000
Total Costs, Net of Accumulated Depreciation	$ 36,185,000
Eldridge Green, Houston, TX | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
Eldridge Green, Houston, TX | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
Liberty Plaza, Addison, TX
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 4,374,000
Initial cost of Buildings Improvements and Equipment	21,146,000
Costs Capitalized (Disposals) Subsequent to Acquisition	11,991,000
Historical Cost of Land	4,279,000
Historical Cost of Buildings Improvements and Equipment	33,232,000
Total	37,511,000
Accumulated Depreciation	15,314,000
Total Costs, Net of Accumulated Depreciation	$ 22,197,000
Liberty Plaza, Addison, TX | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
Liberty Plaza, Addison, TX | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
Park Ten II, Houston, TX
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 1,300,000
Initial cost of Buildings Improvements and Equipment	31,712,000
Costs Capitalized (Disposals) Subsequent to Acquisition	7,258,000
Historical Cost of Land	1,300,000
Historical Cost of Buildings Improvements and Equipment	38,970,000
Total	40,270,000
Accumulated Depreciation	16,870,000
Total Costs, Net of Accumulated Depreciation	$ 23,400,000
Park Ten II, Houston, TX | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
Park Ten II, Houston, TX | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
121 South Eight Street, Minneapolis, MN
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 4,444,000
Initial cost of Buildings Improvements and Equipment	15,214,000
Costs Capitalized (Disposals) Subsequent to Acquisition	30,378,000
Historical Cost of Land	4,444,000
Historical Cost of Buildings Improvements and Equipment	45,592,000
Total	50,036,000
Accumulated Depreciation	16,769,000
Total Costs, Net of Accumulated Depreciation	$ 33,267,000
121 South Eight Street, Minneapolis, MN | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
121 South Eight Street, Minneapolis, MN | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
801 Marquette Avenue South, Minneapolis, MN
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 4,184,000
Costs Capitalized (Disposals) Subsequent to Acquisition	28,280,000
Historical Cost of Land	4,184,000
Historical Cost of Buildings Improvements and Equipment	28,280,000
Total	32,464,000
Accumulated Depreciation	7,216,000
Total Costs, Net of Accumulated Depreciation	$ 25,248,000
801 Marquette Avenue South, Minneapolis, MN | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
801 Marquette Avenue South, Minneapolis, MN | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
Legacy Tennyson Center, Plano, TX
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 3,067,000
Initial cost of Buildings Improvements and Equipment	22,064,000
Costs Capitalized (Disposals) Subsequent to Acquisition	6,166,000
Historical Cost of Land	3,067,000
Historical Cost of Buildings Improvements and Equipment	28,230,000
Total	31,297,000
Accumulated Depreciation	9,713,000
Total Costs, Net of Accumulated Depreciation	$ 21,584,000
Legacy Tennyson Center, Plano, TX | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
Legacy Tennyson Center, Plano, TX | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
Westchase I & II, Houston, TX
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 8,491,000
Initial cost of Buildings Improvements and Equipment	121,508,000
Costs Capitalized (Disposals) Subsequent to Acquisition	24,026,000
Historical Cost of Land	8,491,000
Historical Cost of Buildings Improvements and Equipment	145,534,000
Total	154,025,000
Accumulated Depreciation	42,809,000
Total Costs, Net of Accumulated Depreciation	$ 111,216,000
Westchase I & II, Houston, TX | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
Westchase I & II, Houston, TX | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
1999 Broadway, Denver CO
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 16,334,000
Initial cost of Buildings Improvements and Equipment	137,726,000
Costs Capitalized (Disposals) Subsequent to Acquisition	43,291,000
Historical Cost of Land	16,334,000
Historical Cost of Buildings Improvements and Equipment	181,017,000
Total	197,351,000
Accumulated Depreciation	52,482,000
Total Costs, Net of Accumulated Depreciation	$ 144,869,000
1999 Broadway, Denver CO | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
1999 Broadway, Denver CO | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
1001 17th Street, Denver, CO
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 17,413,000
Initial cost of Buildings Improvements and Equipment	165,058,000
Costs Capitalized (Disposals) Subsequent to Acquisition	37,227,000
Historical Cost of Land	17,413,000
Historical Cost of Buildings Improvements and Equipment	202,285,000
Total	219,698,000
Accumulated Depreciation	53,627,000
Total Costs, Net of Accumulated Depreciation	$ 166,071,000
1001 17th Street, Denver, CO | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
1001 17th Street, Denver, CO | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
Plaza Seven, Minneapolis, MN
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 6,604,000
Initial cost of Buildings Improvements and Equipment	54,240,000
Costs Capitalized (Disposals) Subsequent to Acquisition	14,025,000
Historical Cost of Land	6,604,000
Historical Cost of Buildings Improvements and Equipment	68,265,000
Total	74,869,000
Accumulated Depreciation	16,243,000
Total Costs, Net of Accumulated Depreciation	$ 58,626,000
Plaza Seven, Minneapolis, MN | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
Plaza Seven, Minneapolis, MN | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
600 17th Street, Denver, Co
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 20,876,000
Initial cost of Buildings Improvements and Equipment	99,941,000
Costs Capitalized (Disposals) Subsequent to Acquisition	18,060,000
Historical Cost of Land	20,876,000
Historical Cost of Buildings Improvements and Equipment	118,001,000
Total	138,877,000
Accumulated Depreciation	23,320,000
Total Costs, Net of Accumulated Depreciation	$ 115,557,000
600 17th Street, Denver, Co | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
600 17th Street, Denver, Co | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
Monument Circle, Indianapolis, IN
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 6,416,000
Initial cost of Buildings Improvements and Equipment	13,279,000
Historical Cost of Land	6,416,000
Historical Cost of Buildings Improvements and Equipment	13,279,000
Total	19,695,000
Accumulated Depreciation	341,000
Total Costs, Net of Accumulated Depreciation	$ 19,354,000
Monument Circle, Indianapolis, IN | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
Monument Circle, Indianapolis, IN | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years