Segment Information - Shared Assets (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 27, 2020	Mar. 29, 2019	Mar. 27, 2020	Mar. 29, 2019
Segment Reporting Information [Line Items]
Net sales	$ 455,654	$ 469,309	$ 903,102	$ 921,337
Operating segment Adjusted EBITDA	95,098	84,796	181,973	164,172
Electrical Raceway
Segment Reporting Information [Line Items]
Net sales	339,005	353,119	679,793	696,334
MP&S
Segment Reporting Information [Line Items]
Net sales	116,649	116,190	223,309	225,003
Intersegment Sales
Segment Reporting Information [Line Items]
Net sales	(700)	(395)	(1,288)	(586)
Intersegment Sales | Electrical Raceway
Segment Reporting Information [Line Items]
Net sales	700	395	1,288	586
Intersegment Sales | MP&S
Segment Reporting Information [Line Items]
Net sales	0	0	0	0
Operating Segments | Electrical Raceway
Segment Reporting Information [Line Items]
Operating segment Adjusted EBITDA	78,954	67,375	149,175	135,864
Operating Segments | MP&S
Segment Reporting Information [Line Items]
Operating segment Adjusted EBITDA	$ 16,144	$ 17,421	$ 32,798	$ 28,308