Segment Information - Shared Assets (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 27, 2019	Dec. 28, 2018
Segment Reporting Information [Line Items]
Net sales	$ 447,448	$ 452,028
Operating segment Adjusted EBITDA	86,847	79,376
Electrical Raceway
Segment Reporting Information [Line Items]
Net sales	340,788	343,215
MP&S
Segment Reporting Information [Line Items]
Net sales	106,660	108,813
Intersegment Sales
Segment Reporting Information [Line Items]
Net sales	(588)	(191)
Intersegment Sales | Electrical Raceway
Segment Reporting Information [Line Items]
Net sales	588	191
Intersegment Sales | MP&S
Segment Reporting Information [Line Items]
Net sales	0	0
Operating Segments | Electrical Raceway
Segment Reporting Information [Line Items]
Operating segment Adjusted EBITDA	70,193	68,489
Operating Segments | MP&S
Segment Reporting Information [Line Items]
Operating segment Adjusted EBITDA	$ 16,654	$ 10,887