Industry Segments - Total Assets by Segment (Detail) - USD ($)	Dec. 31, 2015	Dec. 31, 2014
Total assets
Total assets	$ 133,920,000	$ 131,776,000
Operating Segments [Member] | SLPE [Member]
Total assets
Total assets	32,899,000	34,989,000
Operating Segments [Member] | High Power Group [Member]
Total assets
Total assets	30,430,000	33,306,000
Operating Segments [Member] | SL-MTI [Member]
Total assets
Total assets	57,337,000	22,752,000
Unallocated Corporate [Member]
Total assets
Total assets	$ 13,254,000	$ 40,729,000