Business Segment Information (Financial Information By Reportable Segment) (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2018 USD ($)	Apr. 01, 2017 USD ($)	Mar. 31, 2018 USD ($) segment	Apr. 01, 2017 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments | segment			2
Future number of operating segments | segment			3
Total revenue	$ 191,323	$ 193,424	$ 385,485	$ 392,703
Total income from operations	16,610	15,412	33,107	25,702
Test
Segment Reporting Information [Line Items]
Total revenue	110,238	123,840	228,441	254,966
Total income from operations	3,295	6,367	8,904	18,083
Sensors
Segment Reporting Information [Line Items]
Total revenue	81,542	69,584	157,501	137,737
Total income from operations	13,337	9,045	24,225	7,619
Intersegment Eliminations
Segment Reporting Information [Line Items]
Total revenue	(457)	0	(457)	0
Total income from operations	$ (22)	$ 0	$ (22)	$ 0