Segment Information - Unaudited Comparative Results of Segment Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Net sales
Net sales	$ 52,999,000	$ 50,886,000	$ 151,880,000	$ 149,125,000
Income from operations
Income from operations	4,705,000	3,533,000	12,322,000	8,250,000
Operating Segments [Member] | SLPE [Member]
Net sales
Net sales	22,370,000	21,194,000	58,350,000	58,361,000
Income from operations
Income from operations	2,115,000	1,144,000	4,296,000	1,412,000
Operating Segments [Member] | High Power Group [Member]
Net sales
Net sales	16,396,000	15,620,000	51,096,000	47,091,000
Income from operations
Income from operations	1,444,000	1,499,000	5,596,000	4,449,000
Operating Segments [Member] | SL-MTI [Member]
Net sales
Net sales	9,414,000	9,490,000	27,568,000	28,166,000
Income from operations
Income from operations	1,880,000	1,875,000	4,762,000	5,019,000
Operating Segments [Member] | RFL [Member]
Net sales
Net sales	4,819,000	4,582,000	14,866,000	15,507,000
Income from operations
Income from operations	770,000	153,000	2,099,000	1,789,000
Unallocated Corporate Expenses [Member]
Income from operations
Income from operations	$ (1,504,000)	$ (1,138,000)	$ (4,431,000)	$ (4,419,000)