Revenue (Disaggregation) (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 28, 2019	Dec. 29, 2018
Disaggregation of Revenue [Line Items]
Revenue	$ 205,843	$ 203,181
Americas
Disaggregation of Revenue [Line Items]
Revenue	83,971	76,889
Europe
Disaggregation of Revenue [Line Items]
Revenue	49,057	53,975
Asia
Disaggregation of Revenue [Line Items]
Revenue	72,815	72,317
Point-in-time
Disaggregation of Revenue [Line Items]
Revenue	136,845	157,240
Over time
Disaggregation of Revenue [Line Items]
Revenue	68,998	45,941
Product
Disaggregation of Revenue [Line Items]
Revenue	178,858	175,078
Service
Disaggregation of Revenue [Line Items]
Revenue	26,985	28,103
Operating Segments | Test & Simulation
Disaggregation of Revenue [Line Items]
Revenue	120,730	125,560
Operating Segments | Test & Simulation | Americas
Disaggregation of Revenue [Line Items]
Revenue	37,848	39,489
Operating Segments | Test & Simulation | Europe
Disaggregation of Revenue [Line Items]
Revenue	26,515	28,627
Operating Segments | Test & Simulation | Asia
Disaggregation of Revenue [Line Items]
Revenue	56,367	57,444
Operating Segments | Test & Simulation | Point-in-time
Disaggregation of Revenue [Line Items]
Revenue	60,104	79,619
Operating Segments | Test & Simulation | Over time
Disaggregation of Revenue [Line Items]
Revenue	60,626	45,941
Operating Segments | Test & Simulation | Product
Disaggregation of Revenue [Line Items]
Revenue	95,496	98,907
Operating Segments | Test & Simulation | Service
Disaggregation of Revenue [Line Items]
Revenue	25,234	26,653
Operating Segments | Sensors
Disaggregation of Revenue [Line Items]
Revenue	85,535	77,950
Operating Segments | Sensors | Americas
Disaggregation of Revenue [Line Items]
Revenue	46,545	37,729
Operating Segments | Sensors | Europe
Disaggregation of Revenue [Line Items]
Revenue	22,542	25,348
Operating Segments | Sensors | Asia
Disaggregation of Revenue [Line Items]
Revenue	16,448	14,873
Operating Segments | Sensors | Point-in-time
Disaggregation of Revenue [Line Items]
Revenue	77,163	77,950
Operating Segments | Sensors | Over time
Disaggregation of Revenue [Line Items]
Revenue	8,372	0
Operating Segments | Sensors | Product
Disaggregation of Revenue [Line Items]
Revenue	83,774	76,500
Operating Segments | Sensors | Service
Disaggregation of Revenue [Line Items]
Revenue	1,761	1,450
Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenue	(422)	(329)
Intersegment Eliminations | Americas
Disaggregation of Revenue [Line Items]
Revenue	(422)	(329)
Intersegment Eliminations | Europe
Disaggregation of Revenue [Line Items]
Revenue	0	0
Intersegment Eliminations | Asia
Disaggregation of Revenue [Line Items]
Revenue	0	0
Intersegment Eliminations | Point-in-time
Disaggregation of Revenue [Line Items]
Revenue	(422)	(329)
Intersegment Eliminations | Over time
Disaggregation of Revenue [Line Items]
Revenue	0	0
Intersegment Eliminations | Product
Disaggregation of Revenue [Line Items]
Revenue	(412)	(329)
Intersegment Eliminations | Service
Disaggregation of Revenue [Line Items]
Revenue	$ (10)	$ 0