Mortgages and Other Notes Payable - Schedule of Debt (Details) $ in Thousands		12 Months Ended
	Mar. 04, 2021	Dec. 31, 2020 USD ($)	Mar. 05, 2020 a	Dec. 31, 2019 USD ($)
Debt Instrument [Line Items]
Mortgages and other notes payable		$ 242,711		$ 249,854
600 Las Colinas
Debt Instrument [Line Items]
Mortgages and other notes payable		$ 35,589		36,302
Interest rate		5.30%
770 South Post Oak
Debt Instrument [Line Items]
Mortgages and other notes payable		$ 11,871		12,077
Interest rate		4.40%
Bridge View Plaza
Debt Instrument [Line Items]
Mortgages and other notes payable		$ 0		3,824
Interest rate		7.75%
Chelsea
Debt Instrument [Line Items]
Mortgages and other notes payable		$ 8,194		8,749
Interest rate		3.40%
EQK Portage - Land
Debt Instrument [Line Items]
Mortgages and other notes payable		$ 3,350		0
Interest rate		10.00%
Area of land (acres) | a			49.2
HSW Partners
Debt Instrument [Line Items]
Mortgages and other notes payable		$ 17,790		17,359
Interest rate		9.50%
Farnham Park
Debt Instrument [Line Items]
Mortgages and other notes payable		$ 0		9,144
Interest rate		3.39%
Forest Grove
Debt Instrument [Line Items]
Mortgages and other notes payable		$ 7,333		1,390
Interest rate		3.75%
Forest Grove | Prime Rate
Debt Instrument [Line Items]
Variable interest rate		0.50%
Landing Bayou
Debt Instrument [Line Items]
Mortgages and other notes payable		$ 14,643		15,467
Interest rate		3.50%
Athens
Debt Instrument [Line Items]
Mortgages and other notes payable		$ 1,155		1,155
Interest rate		5.90%
Legacy at Pleasant Grove
Debt Instrument [Line Items]
Mortgages and other notes payable		$ 13,653		13,944
Interest rate		3.60%
McKinney 36 Land
Debt Instrument [Line Items]
Mortgages and other notes payable		$ 820		944
Interest rate		8.00%
New Concept Energy
Debt Instrument [Line Items]
Mortgages and other notes payable		$ 3,542		4,000
Interest rate		6.00%
Overlook at Allenville Phase II
Debt Instrument [Line Items]
Mortgages and other notes payable		$ 15,621		15,798
Interest rate		3.80%
Parc at Denham Springs II
Debt Instrument [Line Items]
Mortgages and other notes payable		$ 16,128		14,785
Interest rate		4.10%
Standford Center
Debt Instrument [Line Items]
Mortgages and other notes payable		$ 39,093		39,255
Interest rate		6.00%
Sugar Mill Phase III
Debt Instrument [Line Items]
Mortgages and other notes payable		$ 9,298		5,908
Interest rate		4.50%
Toulon
Debt Instrument [Line Items]
Mortgages and other notes payable		$ 13,975		14,219
Interest rate		3.20%
Villager
Debt Instrument [Line Items]
Mortgages and other notes payable		$ 0		556
Interest rate		2.50%
Villas at Bon Secour
Debt Instrument [Line Items]
Mortgages and other notes payable		$ 10,280		11,026
Interest rate		4.00%
Vista Ridge
Debt Instrument [Line Items]
Mortgages and other notes payable		$ 9,979		10,122
Interest rate		4.00%
Windmill Farms
Debt Instrument [Line Items]
Mortgages and other notes payable		$ 10,397		$ 13,830
Interest rate		6.00%
Windmill Farms | Subsequent Event
Debt Instrument [Line Items]
Interest rate	5.00%