Revenue (Disaggregation) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 27, 2020	Jun. 29, 2019	Jun. 27, 2020	Jun. 29, 2019
Disaggregation of Revenue [Line Items]
Revenue	$ 196,225	$ 232,209	$ 613,531	$ 668,436
Americas
Disaggregation of Revenue [Line Items]
Revenue	74,420	89,907	242,382	256,809
Europe
Disaggregation of Revenue [Line Items]
Revenue	56,802	61,131	173,161	172,295
Asia
Disaggregation of Revenue [Line Items]
Revenue	65,003	81,171	197,988	239,332
Point-in-time
Disaggregation of Revenue [Line Items]
Revenue	132,422	172,875	404,187	503,693
Over time
Disaggregation of Revenue [Line Items]
Revenue	63,803	59,334	209,344	164,743
Product
Disaggregation of Revenue [Line Items]
Revenue	175,223	205,528	537,304	587,297
Service
Disaggregation of Revenue [Line Items]
Revenue	21,002	26,681	76,227	81,139
Operating Segments | Test & Simulation
Disaggregation of Revenue [Line Items]
Revenue	116,404	148,328	362,631	424,920
Operating Segments | Test & Simulation | Americas
Disaggregation of Revenue [Line Items]
Revenue	32,821	47,892	110,044	138,780
Operating Segments | Test & Simulation | Europe
Disaggregation of Revenue [Line Items]
Revenue	36,951	34,137	104,601	92,300
Operating Segments | Test & Simulation | Asia
Disaggregation of Revenue [Line Items]
Revenue	46,632	66,299	147,986	193,840
Operating Segments | Test & Simulation | Point-in-time
Disaggregation of Revenue [Line Items]
Revenue	60,792	95,247	178,512	273,226
Operating Segments | Test & Simulation | Over time
Disaggregation of Revenue [Line Items]
Revenue	55,612	53,081	184,119	151,694
Operating Segments | Test & Simulation | Product
Disaggregation of Revenue [Line Items]
Revenue	96,870	123,573	294,654	348,992
Operating Segments | Test & Simulation | Service
Disaggregation of Revenue [Line Items]
Revenue	19,534	24,755	67,977	75,928
Operating Segments | Sensors
Disaggregation of Revenue [Line Items]
Revenue	80,222	84,231	251,955	244,556
Operating Segments | Sensors | Americas
Disaggregation of Revenue [Line Items]
Revenue	42,000	42,365	133,393	119,069
Operating Segments | Sensors | Europe
Disaggregation of Revenue [Line Items]
Revenue	19,851	26,994	68,560	79,995
Operating Segments | Sensors | Asia
Disaggregation of Revenue [Line Items]
Revenue	18,371	14,872	50,002	45,492
Operating Segments | Sensors | Point-in-time
Disaggregation of Revenue [Line Items]
Revenue	72,031	77,978	226,730	231,507
Operating Segments | Sensors | Over time
Disaggregation of Revenue [Line Items]
Revenue	8,191	6,253	25,225	13,049
Operating Segments | Sensors | Product
Disaggregation of Revenue [Line Items]
Revenue	78,739	82,305	243,674	239,345
Operating Segments | Sensors | Service
Disaggregation of Revenue [Line Items]
Revenue	1,483	1,926	8,281	5,211
Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenue	(401)	(350)	(1,055)	(1,040)
Intersegment Eliminations | Americas
Disaggregation of Revenue [Line Items]
Revenue	(401)	(350)	(1,055)	(1,040)
Intersegment Eliminations | Europe
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Intersegment Eliminations | Asia
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Intersegment Eliminations | Point-in-time
Disaggregation of Revenue [Line Items]
Revenue	(401)	(350)	(1,055)	(1,040)
Intersegment Eliminations | Over time
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Intersegment Eliminations | Product
Disaggregation of Revenue [Line Items]
Revenue	(386)	(350)	(1,024)	(1,040)
Intersegment Eliminations | Service
Disaggregation of Revenue [Line Items]
Revenue	$ (15)	$ 0	$ (31)	$ 0