Business segment information - Schedule of Business Segment Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Net sales:
Total net sales	$ 161,287	$ 166,562	$ 140,815
Operating income (loss):
Total operating income	25,435	25,436	20,526
Interest income	4,168	1,877	1,197
Income before income taxes	29,603	27,313	21,723
Depreciation and amortization	3,973	3,977	3,839
Total capital expenditures	1,130	3,695	4,094
Security Products
Net sales:
Total net sales	121,182	114,519	105,124
Operating income (loss):
Capital expenditures:	970	2,015	1,044
Marine Components
Net sales:
Total net sales	40,105	52,043	35,691
Operating income (loss):
Capital expenditures:	160	1,680	3,050
Operating Segments | Security Products
Operating income (loss):
Total operating income	24,941	22,744	21,622
Depreciation and amortization	2,748	2,801	2,890
Operating Segments | Marine Components
Operating income (loss):
Total operating income	7,218	9,561	5,591
Depreciation and amortization	1,217	1,167	940
Corporate
Operating income (loss):
Total operating income	(6,724)	(6,869)	(6,687)
Depreciation and amortization	$ 8	$ 9	$ 9