Business Segment Information (Financial Information by Reportable Segment) (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 27, 2020 USD ($)	Jun. 29, 2019 USD ($)	Jun. 27, 2020 USD ($) segment	Jun. 29, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments | segment			2
Total revenue	$ 196,225	$ 232,209	$ 613,531	$ 668,436
Total income from operations	12,643	23,001	35,771	65,141
Test & Simulation
Segment Reporting Information [Line Items]
Restructuring expense	(2,745)		(8,883)
Operating Segments | Test & Simulation
Segment Reporting Information [Line Items]
Total revenue	116,404	148,328	362,631	424,920
Total income from operations	(292)	11,424	5,899	31,439
Operating Segments | Sensors
Segment Reporting Information [Line Items]
Total revenue	80,222	84,231	251,955	244,556
Total income from operations	12,935	11,556	29,873	33,694
Intersegment Eliminations
Segment Reporting Information [Line Items]
Total revenue	(401)	(350)	(1,055)	(1,040)
Total income from operations	$ 0	$ 21	$ (1)	$ 8