Industry Segments - Comparative Results of Segment Information (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net sales
Net sales	$ 52,784,000	$ 49,675,000	$ 50,719,000	$ 46,684,000	$ 53,277,000	$ 50,725,000	$ 51,669,000	$ 48,746,000	$ 199,862,000	$ 204,417,000	$ 184,658,000
Income from operations
Income from operations									17,986,000	19,562,000	10,235,000
Amortization of deferred financing costs									(191,000)	(94,000)	(83,000)
Interest income									25,000	13,000	12,000
Interest expense									(123,000)	(27,000)	(61,000)
Other gain (loss), net									340,000	1,769,000	(78,000)
Income from continuing operations before income taxes	$ 5,361,000	$ 2,904,000	$ 5,624,000	$ 4,148,000	$ 4,843,000	$ 4,211,000	$ 7,998,000	$ 4,171,000	18,037,000	21,223,000	10,025,000
Unallocated Corporate [Member]
Income from operations
Income from operations									(7,739,000)	(7,000,000)	(5,731,000)
Segment Reconciling Items [Member]
Income from operations
Amortization of deferred financing costs									(191,000)	(94,000)	(83,000)
Interest income									25,000	13,000	12,000
Interest expense									(123,000)	(27,000)	(61,000)
Other gain (loss), net									340,000	1,769,000	(78,000)
SLPE [Member]
Net sales
Net sales									70,728,000	74,593,000	78,177,000
SLPE [Member] | Operating Segments [Member]
Income from operations
Income from operations									10,023,000	7,217,000	6,558,000
High Power Group [Member]
Net sales
Net sales									69,621,000	85,332,000	68,752,000
High Power Group [Member] | Operating Segments [Member]
Income from operations
Income from operations									7,658,000	12,175,000	2,206,000
SL-MTI [Member]
Net sales
Net sales									59,513,000	44,492,000	37,729,000
SL-MTI [Member] | Operating Segments [Member]
Income from operations
Income from operations									$ 8,044,000	$ 7,170,000	$ 7,202,000