Basis of presentation and summary of significant accounting policies - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Schedule Of Accounting Policies [Line Items]
General and administrative expense	$ 332,000	$ 311,000	$ 1,007,000	$ 976,000
Loss from sale of discontinued operations	(2,000)	(55,000)	(22,000)	(106,000)
Income tax benefit	$ 218,000	168,000	662,000	555,000
Net cash provided by operating activities			2,059,000	1,847,000
Cash used in investing activities			$ (22,000)	(168,000)
Reclassification of Prior Period [Member]
Schedule Of Accounting Policies [Line Items]
General and administrative expense		75,000		145,000
Loss from sale of discontinued operations		(55,000)		(106,000)
Income tax benefit		$ (20,000)		(39,000)
Net cash provided by operating activities				106,000
Cash used in investing activities				$ 106,000