Segment Information - Shared Assets (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 26, 2020	Jun. 28, 2019	Jun. 26, 2020	Jun. 28, 2019
Segment Reporting Information [Line Items]
Net sales	$ 384,899	$ 493,491	$ 1,288,001	$ 1,414,828
Operating segment Adjusted EBITDA	69,698	97,316	251,671	261,488
Electrical Raceway
Segment Reporting Information [Line Items]
Net sales	285,412	372,895	965,205	1,069,229
MP&S
Segment Reporting Information [Line Items]
Net sales	99,487	120,596	322,796	345,599
Intersegment Sales
Segment Reporting Information [Line Items]
Net sales	(634)	(334)	(1,922)	(920)
Intersegment Sales | Electrical Raceway
Segment Reporting Information [Line Items]
Net sales	634	334	1,922	920
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	57,455	76,721	206,630	212,585
Operating Segments | MP&S
Segment Reporting Information [Line Items]
Operating segment Adjusted EBITDA	$ 12,243	$ 20,595	$ 45,041	$ 48,903