Business Segment Information - Financial Information by Reportable Segment (Details) $ in Thousands	3 Months Ended
	Jan. 02, 2021 USD ($) segment	Dec. 28, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments | segment	2
Total revenue	$ 198,804	$ 205,843
Total income from operations	4,631	15,158
Operating Segments | Test & Simulation
Segment Reporting Information [Line Items]
Total revenue	113,223	120,730
Total income from operations	(2,951)	6,996
Operating Segments | Sensors
Segment Reporting Information [Line Items]
Total revenue	85,803	85,535
Total income from operations	7,581	8,159
Intersegment eliminations
Segment Reporting Information [Line Items]
Total revenue	(222)	(422)
Total income from operations	$ 1	$ 3