Business Segment Information - Financial Information by Reportable Segment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 26, 2020	Sep. 28, 2019	Sep. 26, 2020	Sep. 28, 2019
Segment Reporting Information [Line Items]
Revenue	$ 150,371	$ 181,101	$ 471,155	$ 534,162
Operating Income	10,265	14,603	33,916	41,055
Depreciation and Amortization Expenses	7,078	6,992	21,741	20,751
Capital Expenditures	2,382	4,515	7,918	14,928
Electronic Systems
Segment Reporting Information [Line Items]
Revenue	103,470	90,588	293,540	264,045
Structural Systems
Segment Reporting Information [Line Items]
Revenue	46,901	90,513	177,615	270,117
Operating Segments
Segment Reporting Information [Line Items]
Operating Income	16,636	22,534	53,800	63,949
Operating Segments | Electronic Systems
Segment Reporting Information [Line Items]
Operating Income	14,867	9,657	40,427	28,750
Depreciation and Amortization Expenses	3,492	3,569	10,591	10,602
Capital Expenditures	586	1,768	3,518	4,820
Operating Segments | Structural Systems
Segment Reporting Information [Line Items]
Operating Income	1,769	12,877	13,373	35,199
Depreciation and Amortization Expenses	3,528	3,350	10,956	9,750
Capital Expenditures	1,796	2,747	4,400	10,108
Segment Reconciling Items
Segment Reporting Information [Line Items]
Corporate General and Administrative Expenses	(6,371)	(7,931)	(19,884)	(22,894)
Corporate Administration
Segment Reporting Information [Line Items]
Depreciation and Amortization Expenses	58	73	194	399
Capital Expenditures	$ 0	$ 0	$ 0	$ 0