Goodwill and Intangible Assets - Change in Carrying Amount (Details) $ in Thousands	9 Months Ended
	Jun. 26, 2020 USD ($)
Goodwill [Roll Forward]
Balance at beginning of period	$ 186,231
Exchange rate effects	378
Balance at end of period	186,609
Electrical Raceway
Goodwill [Roll Forward]
Balance at beginning of period	149,668
Exchange rate effects	378
Balance at end of period	150,046
Mechanical Products & Solutions
Goodwill [Roll Forward]
Balance at beginning of period	36,563
Exchange rate effects	0
Balance at end of period	$ 36,563