Business Segment Information - Financial Information by Reportable Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Oct. 01, 2016	Sep. 30, 2017	Oct. 01, 2016
Segment Reporting Information [Line Items]
Net Revenues	$ 138,690	$ 132,571	$ 415,925	$ 408,156
Operating Income	7,195	8,052	17,766	19,611
Depreciation and Amortization Expenses	5,619	6,089	17,149	17,420
Capital Expenditures	6,369	4,502	22,248	11,850
Operating Segments
Segment Reporting Information [Line Items]
Operating Income	11,700	12,493	32,305	33,116
Operating Segments | Structural Systems
Segment Reporting Information [Line Items]
Net Revenues	59,685	60,931	176,372	185,642
Operating Income	3,466	5,893	8,147	13,347
Depreciation and Amortization Expenses	2,220	2,851	6,879	6,683
Capital Expenditures	4,449	3,555	17,217	10,149
Operating Segments | Electronic Systems
Segment Reporting Information [Line Items]
Net Revenues	79,005	71,640	239,553	222,514
Operating Income	8,234	6,600	24,158	19,769
Depreciation and Amortization Expenses	3,345	3,232	10,207	10,661
Capital Expenditures	1,793	947	4,256	1,701
Segment Reconciling Items
Segment Reporting Information [Line Items]
Corporate General and Administrative Expenses	(4,505)	(4,441)	(14,539)	(13,505)
Corporate Administration
Segment Reporting Information [Line Items]
Depreciation and Amortization Expenses	54	6	63	76
Capital Expenditures	$ 127	$ 0	$ 775	$ 0