Business Segment Information (Financial Information by Reportable Segment) (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 29, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 29, 2019 USD ($) segment	Jun. 30, 2018 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments | segment			2
Total revenue	$ 232,209	$ 194,668	$ 668,436	$ 580,153
Total income from operations	23,001	16,264	65,141	49,371
Operating Segments | Test & Simulation
Segment Reporting Information [Line Items]
Total revenue	148,328	116,055	424,920	344,496
Total income from operations	11,424	3,873	31,439	12,777
Operating Segments | Sensors
Segment Reporting Information [Line Items]
Total revenue	84,231	79,000	244,556	236,501
Total income from operations	11,556	12,398	33,694	36,623
Intersegment Eliminations
Segment Reporting Information [Line Items]
Total revenue	(350)	(387)	(1,040)	(844)
Total income from operations	$ 21	$ (7)	$ 8	$ (29)