Income Taxes, Continuing Operations - Deferred Tax Assets and Liabilities (Detail) - USD ($)	Mar. 31, 2021	Dec. 31, 2020
Gross deferred tax liabilities:
Property having a financial statement basis in excess of tax basis	$ 361,000	$ 361,000
Accounts receivable	116,000	98,000
Deferred income - conversion to cash basis of accounting for tax purposes	52,000	56,000
Insurance premiums and accrued leasing revenues	24,000	19,000
Gross deferred tax liabilities	553,000	534,000
Gross deferred tax assets:
Allowance for doubtful accounts	(104,000)	(91,000)
Prepaid rent	(54,000)	(24,000)
Accounts payable and accrued expenses	(77,000)	(75,000)
Accrued property taxes	(67,000)	(56,000)
Deferred income, Parcel 20	(61,000)	(54,000)
Gross deferred tax assets	(363,000)	(300,000)
Deferred tax liabilities, net of deferred tax assets	$ 190,000	$ 234,000