Business Segment Information (Financial Information by Reportable Segment) (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 30, 2019 USD ($)	Mar. 31, 2018 USD ($)	Mar. 30, 2019 USD ($) segment	Mar. 31, 2018 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments | segment			2
Total revenue	$ 233,046	$ 191,323	$ 436,227	$ 385,485
Total income from operations	24,174	16,610	42,140	33,107
Intersegment Eliminations
Segment Reporting Information [Line Items]
Total revenue	(361)	(457)	(690)	(457)
Total income from operations	(14)	(22)	(13)	(22)
Operating Segments | Test & Simulation
Segment Reporting Information [Line Items]
Total revenue	151,032	110,238	276,592	228,441
Total income from operations	12,684	3,295	20,015	8,904
Operating Segments | Sensors
Segment Reporting Information [Line Items]
Total revenue	82,375	81,542	160,325	157,501
Total income from operations	$ 11,504	$ 13,337	$ 22,138	$ 24,225