Business and Geographic Segments - Business Segment Information by Geographical Areas (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net sales:
Net sales	$ 25,100	$ 27,000	$ 30,000	$ 29,900	$ 26,300	$ 28,400	$ 27,100	$ 27,100	$ 112,035	$ 108,920	$ 108,994
Total assets	150,959				143,980				150,959	143,980	134,792
Operating Segments | Security Products
Net sales:
Net sales									96,600	94,693	95,614
Total assets	72,961				73,345				72,961	73,345	72,561
Operating Segments | Marine Components
Net sales:
Net sales									15,435	14,227	13,380
Total assets	11,704				12,209				11,704	12,209	12,761
Corporate and eliminations
Net sales:
Total assets	$ 66,294				$ 58,426				66,294	58,426	49,470
Point Of Destination | United States
Net sales:
Net sales									103,646	98,526	103,737
Point Of Destination | Canada
Net sales:
Net sales									5,353	7,515	2,352
Point Of Destination | Mexico
Net sales:
Net sales									1,486	1,315	1,334
Point Of Destination | Other
Net sales:
Net sales									$ 1,550	$ 1,564	$ 1,571