Restructuring Charges and Asset Impairments - Narrative (Details) - USD ($)	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 25, 2015	Sep. 26, 2014
Restructuring Cost and Reserve [Line Items]
Charges	$ 1,522,000	$ 4,278,000	$ 4,789,000
Restructuring reserve	737,000	1,380,000	4,413,000	$ 1,592,000
Asset impairment charges	0	129,000	27,937,000
Exit of Fence and Sprinkler
Restructuring Cost and Reserve [Line Items]
Inventory write-down			4,518,000
One-time Termination Benefits
Restructuring Cost and Reserve [Line Items]
Charges	297	778
Prepaid Shop Supplies
Restructuring Cost and Reserve [Line Items]
Asset impairment charges		129,000	27,937,000
Property, Plant and Equipment | Exit of Fence and Sprinkler
Restructuring Cost and Reserve [Line Items]
Asset impairment charges			19,495,000
Prepaid Supplies | Exit of Fence and Sprinkler
Restructuring Cost and Reserve [Line Items]
Asset impairment charges			664,000
Operating Segments | Electrical Raceway | Severance
Restructuring Cost and Reserve [Line Items]
Charges	527,000	807,000	0
Restructuring reserve	$ 449,000	$ 841,000	$ 206,000	$ 593,000