Industry Segments - Unaudited Comparative Results of Segment Information (Detail) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net sales
Net sales	$ 51,452,000	$ 50,886,000	$ 48,899,000	$ 49,340,000	$ 51,379,000	$ 52,092,000	$ 56,266,000	$ 52,594,000	$ 200,577,000	$ 212,331,000	$ 189,768,000
Income from operations
Income from operations									12,901,000	18,534,000	13,248,000
Amortization of deferred financing costs									(138,000)	(218,000)	(252,000)
Interest income									5,000	3,000	2,000
Interest expense									(48,000)	(179,000)	(86,000)
Fire related gain (loss), net										277,000	(109,000)
Other gain (loss), net									302,000
Income from continuing operations before income taxes	4,783,000	3,792,000	2,137,000	2,310,000	4,304,000	3,473,000	5,758,000	4,882,000	13,022,000	18,417,000	12,803,000
SLPE [Member]
Net sales
Net sales									77,869,000	91,066,000	79,615,000
Income from operations
Income from operations									2,487,000	7,825,000	6,389,000
High Power Group [Member]
Net sales
Net sales									65,283,000	63,027,000	56,494,000
Income from operations
Income from operations									6,822,000	6,940,000	5,418,000
SL-MTI [Member]
Net sales
Net sales									36,223,000	35,413,000	31,261,000
Income from operations
Income from operations									6,292,000	6,219,000	4,801,000
RFL [Member]
Net sales
Net sales									21,202,000	22,825,000	22,398,000
Income from operations
Income from operations									2,763,000	3,189,000	2,990,000
Unallocated Corporate Expenses [Member]
Income from operations
Income from operations									$ (5,463,000)	$ (5,639,000)	$ (6,350,000)