Schedule III - Real Estate and Accumulated Depreciation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017
Initial Cost
Land			$ 15,549
Building and Improvements			63,208
Costs Capitalized Subsequent to Acquisition
Improvements (net)			16,389
Carrying Costs			0
Gross Amount at which Carried at End of Period
Land			15,549
Building and Improvements			79,597
Total	$ 92,338	$ 0	95,146
Accumulated Depreciation			35,980
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance at beginning of period	92,338	0
Additions during the period:
Acquisitions	2,550	92,338
Improvements	1,265	0
Real estate, total additions	3,815	92,338
Deductions - cost of real estate sold or retired	(1,007)	0
Balance at close of period	95,146	$ 92,338
Aggregate cost of real estate for federal income tax purposes			84,646
9101 LBJ Freeway [Member]
Initial Cost
Land			1,597
Building and Improvements			6,078
Costs Capitalized Subsequent to Acquisition
Improvements (net)			1,128
Carrying Costs			0
Gross Amount at which Carried at End of Period
Land			1,597
Building and Improvements			7,206
Total	8,803		8,803
Accumulated Depreciation			2,634
Additions during the period:
Balance at close of period	$ 8,803
9101 LBJ Freeway [Member] | Minimum [Member]
Gross Amount at which Carried at End of Period
Depreciation Life	5 years
9101 LBJ Freeway [Member] | Maximum [Member]
Gross Amount at which Carried at End of Period
Depreciation Life	39 years
Corporate Park Northwest [Member]
Initial Cost
Land			1,534
Building and Improvements			6,306
Costs Capitalized Subsequent to Acquisition
Improvements (net)			2,268
Carrying Costs			0
Gross Amount at which Carried at End of Period
Land			1,534
Building and Improvements			8,574
Total	$ 10,108		10,108
Accumulated Depreciation			3,679
Additions during the period:
Balance at close of period	$ 10,108
Corporate Park Northwest [Member] | Minimum [Member]
Gross Amount at which Carried at End of Period
Depreciation Life	5 years
Corporate Park Northwest [Member] | Maximum [Member]
Gross Amount at which Carried at End of Period
Depreciation Life	39 years
Corporate Park West [Member]
Initial Cost
Land			2,555
Building and Improvements			10,267
Costs Capitalized Subsequent to Acquisition
Improvements (net)			1,615
Carrying Costs			0
Gross Amount at which Carried at End of Period
Land			2,555
Building and Improvements			11,882
Total	$ 14,437		14,437
Accumulated Depreciation			4,959
Additions during the period:
Balance at close of period	$ 14,437
Corporate Park West [Member] | Minimum [Member]
Gross Amount at which Carried at End of Period
Depreciation Life	5 years
Corporate Park West [Member] | Maximum [Member]
Gross Amount at which Carried at End of Period
Depreciation Life	39 years
Corporate Park Woodland [Member]
Initial Cost
Land			652
Building and Improvements			5,330
Costs Capitalized Subsequent to Acquisition
Improvements (net)			830
Carrying Costs			0
Gross Amount at which Carried at End of Period
Land			652
Building and Improvements			6,160
Total	$ 6,812		6,812
Accumulated Depreciation			3,331
Additions during the period:
Balance at close of period	$ 6,812
Corporate Park Woodland [Member] | Minimum [Member]
Gross Amount at which Carried at End of Period
Depreciation Life	5 years
Corporate Park Woodland [Member] | Maximum [Member]
Gross Amount at which Carried at End of Period
Depreciation Life	39 years
Corporate Park Woodland II [Member]
Initial Cost
Land			2,758
Building and Improvements			0
Costs Capitalized Subsequent to Acquisition
Improvements (net)			26
Carrying Costs			0
Gross Amount at which Carried at End of Period
Land			2,758
Building and Improvements			26
Total	$ 2,784		2,784
Accumulated Depreciation			5
Additions during the period:
Balance at close of period	$ 2,784
Corporate Park Woodland II [Member] | Minimum [Member]
Gross Amount at which Carried at End of Period
Depreciation Life	5 years
Corporate Park Woodland II [Member] | Maximum [Member]
Gross Amount at which Carried at End of Period
Depreciation Life	39 years
Dairy Ashford [Member]
Initial Cost
Land			226
Building and Improvements			1,211
Costs Capitalized Subsequent to Acquisition
Improvements (net)			49
Carrying Costs			0
Gross Amount at which Carried at End of Period
Land			226
Building and Improvements			1,260
Total	$ 1,486		1,486
Accumulated Depreciation			686
Additions during the period:
Balance at close of period	$ 1,486
Dairy Ashford [Member] | Minimum [Member]
Gross Amount at which Carried at End of Period
Depreciation Life	5 years
Dairy Ashford [Member] | Maximum [Member]
Gross Amount at which Carried at End of Period
Depreciation Life	39 years
Holly Hall Industrial Park [Member]
Initial Cost
Land			608
Building and Improvements			2,516
Costs Capitalized Subsequent to Acquisition
Improvements (net)			395
Carrying Costs			0
Gross Amount at which Carried at End of Period
Land			608
Building and Improvements			2,911
Total	$ 3,519		3,519
Accumulated Depreciation			1,356
Additions during the period:
Balance at close of period	$ 3,519
Holly Hall Industrial Park [Member] | Minimum [Member]
Gross Amount at which Carried at End of Period
Depreciation Life	5 years
Holly Hall Industrial Park [Member] | Maximum [Member]
Gross Amount at which Carried at End of Period
Depreciation Life	39 years
Holly Knight [Member]
Initial Cost
Land			320
Building and Improvements			1,293
Costs Capitalized Subsequent to Acquisition
Improvements (net)			402
Carrying Costs			0
Gross Amount at which Carried at End of Period
Land			320
Building and Improvements			1,695
Total	$ 2,015		2,015
Accumulated Depreciation			1,090
Additions during the period:
Balance at close of period	$ 2,015
Holly Knight [Member] | Minimum [Member]
Gross Amount at which Carried at End of Period
Depreciation Life	5 years
Holly Knight [Member] | Maximum [Member]
Gross Amount at which Carried at End of Period
Depreciation Life	39 years
Interstate 10 Warehouse [Member]
Initial Cost
Land			208
Building and Improvements			3,700
Costs Capitalized Subsequent to Acquisition
Improvements (net)			495
Carrying Costs			0
Gross Amount at which Carried at End of Period
Land			208
Building and Improvements			4,195
Total	$ 4,403		4,403
Accumulated Depreciation			2,852
Additions during the period:
Balance at close of period	$ 4,403
Interstate 10 Warehouse [Member] | Minimum [Member]
Gross Amount at which Carried at End of Period
Depreciation Life	5 years
Interstate 10 Warehouse [Member] | Maximum [Member]
Gross Amount at which Carried at End of Period
Depreciation Life	39 years
Main Park [Member]
Initial Cost
Land			1,328
Building and Improvements			2,721
Costs Capitalized Subsequent to Acquisition
Improvements (net)			1,113
Carrying Costs			0
Gross Amount at which Carried at End of Period
Land			1,328
Building and Improvements			3,834
Total	$ 5,162		5,162
Accumulated Depreciation			1,957
Additions during the period:
Balance at close of period	$ 5,162
Main Park [Member] | Minimum [Member]
Gross Amount at which Carried at End of Period
Depreciation Life	5 years
Main Park [Member] | Maximum [Member]
Gross Amount at which Carried at End of Period
Depreciation Life	39 years
Plaza Park [Member]
Initial Cost
Land			902
Building and Improvements			3,294
Costs Capitalized Subsequent to Acquisition
Improvements (net)			1,141
Carrying Costs			0
Gross Amount at which Carried at End of Period
Land			902
Building and Improvements			4,435
Total	$ 5,337		5,337
Accumulated Depreciation			2,352
Additions during the period:
Balance at close of period	$ 5,337
Plaza Park [Member] | Minimum [Member]
Gross Amount at which Carried at End of Period
Depreciation Life	5 years
Plaza Park [Member] | Maximum [Member]
Gross Amount at which Carried at End of Period
Depreciation Life	39 years
Uptown Tower [Member]
Initial Cost
Land			1,621
Building and Improvements			15,551
Costs Capitalized Subsequent to Acquisition
Improvements (net)			4,794
Carrying Costs			0
Gross Amount at which Carried at End of Period
Land			1,621
Building and Improvements			20,345
Total	$ 21,966		21,966
Accumulated Depreciation			7,384
Additions during the period:
Balance at close of period	$ 21,966
Amount of encumbrances			16,500
Uptown Tower [Member] | Minimum [Member]
Gross Amount at which Carried at End of Period
Depreciation Life	5 years
Uptown Tower [Member] | Maximum [Member]
Gross Amount at which Carried at End of Period
Depreciation Life	39 years
Westbelt Plaza [Member]
Initial Cost
Land			568
Building and Improvements			2,165
Costs Capitalized Subsequent to Acquisition
Improvements (net)			958
Carrying Costs			0
Gross Amount at which Carried at End of Period
Land			568
Building and Improvements			3,123
Total	$ 3,691		3,691
Accumulated Depreciation			1,981
Additions during the period:
Balance at close of period	$ 3,691
Westbelt Plaza [Member] | Minimum [Member]
Gross Amount at which Carried at End of Period
Depreciation Life	5 years
Westbelt Plaza [Member] | Maximum [Member]
Gross Amount at which Carried at End of Period
Depreciation Life	39 years
Westgate Service Center [Member]
Initial Cost
Land			672
Building and Improvements			2,776
Costs Capitalized Subsequent to Acquisition
Improvements (net)			1,175
Carrying Costs			0
Gross Amount at which Carried at End of Period
Land			672
Building and Improvements			3,951
Total	$ 4,623		4,623
Accumulated Depreciation			1,714
Additions during the period:
Balance at close of period	$ 4,623
Westgate Service Center [Member] | Minimum [Member]
Gross Amount at which Carried at End of Period
Depreciation Life	5 years
Westgate Service Center [Member] | Maximum [Member]
Gross Amount at which Carried at End of Period
Depreciation Life	39 years
Various Pillarstone Properties [Member]
Additions during the period:
Amount of encumbrances			$ 37,000