Revenue (Disaggregation) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 29, 2019	Jun. 30, 2018	Jun. 29, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Revenue	$ 232,209	$ 194,668	$ 668,436	$ 580,153
Americas
Disaggregation of Revenue [Line Items]
Revenue	89,907		256,809
Europe
Disaggregation of Revenue [Line Items]
Revenue	61,131		172,295
Asia
Disaggregation of Revenue [Line Items]
Revenue	81,171		239,332
Point-in-time
Disaggregation of Revenue [Line Items]
Revenue	172,875		503,693
Over time
Disaggregation of Revenue [Line Items]
Revenue	59,334		164,743
Product
Disaggregation of Revenue [Line Items]
Revenue	205,528	168,651	587,297	503,345
Service
Disaggregation of Revenue [Line Items]
Revenue	26,681	26,017	81,139	76,808
Operating Segments | Test & Simulation
Disaggregation of Revenue [Line Items]
Revenue	148,328	116,055	424,920	344,496
Operating Segments | Test & Simulation | Americas
Disaggregation of Revenue [Line Items]
Revenue	47,892		138,780
Operating Segments | Test & Simulation | Europe
Disaggregation of Revenue [Line Items]
Revenue	34,137		92,300
Operating Segments | Test & Simulation | Asia
Disaggregation of Revenue [Line Items]
Revenue	66,299		193,840
Operating Segments | Test & Simulation | Point-in-time
Disaggregation of Revenue [Line Items]
Revenue	95,247		273,226
Operating Segments | Test & Simulation | Over time
Disaggregation of Revenue [Line Items]
Revenue	53,081		151,694
Operating Segments | Test & Simulation | Product
Disaggregation of Revenue [Line Items]
Revenue	123,573		348,992
Operating Segments | Test & Simulation | Service
Disaggregation of Revenue [Line Items]
Revenue	24,755		75,928
Operating Segments | Sensors
Disaggregation of Revenue [Line Items]
Revenue	84,231	79,000	244,556	236,501
Operating Segments | Sensors | Americas
Disaggregation of Revenue [Line Items]
Revenue	42,365		119,069
Operating Segments | Sensors | Europe
Disaggregation of Revenue [Line Items]
Revenue	26,994		79,995
Operating Segments | Sensors | Asia
Disaggregation of Revenue [Line Items]
Revenue	14,872		45,492
Operating Segments | Sensors | Point-in-time
Disaggregation of Revenue [Line Items]
Revenue	77,978		231,507
Operating Segments | Sensors | Over time
Disaggregation of Revenue [Line Items]
Revenue	6,253		13,049
Operating Segments | Sensors | Product
Disaggregation of Revenue [Line Items]
Revenue	82,305		239,345
Operating Segments | Sensors | Service
Disaggregation of Revenue [Line Items]
Revenue	1,926		5,211
Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenue	(350)	$ (387)	(1,040)	$ (844)
Intersegment Eliminations | Americas
Disaggregation of Revenue [Line Items]
Revenue	(350)		(1,040)
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	(350)		(1,040)
Intersegment Eliminations | Over time
Disaggregation of Revenue [Line Items]
Revenue	0		0
Intersegment Eliminations | Product
Disaggregation of Revenue [Line Items]
Revenue	(350)		(1,040)
Intersegment Eliminations | Service
Disaggregation of Revenue [Line Items]
Revenue	$ 0		$ 0