Disaggregation of Revenue - Schedule of Revenue Disaggregation for Customer Type (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 26, 2020	Dec. 28, 2019
Disaggregation Of Revenue [Line Items]
Total revenues	$ 305,191	$ 333,878
Retail [Member] | Residential [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	174,711	196,886
Retail [Member] | Commercial [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	79,440	83,335
Retail [Member] | Industrial [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	25,795	26,599
Retail [Member] | Agricultural [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	11,138	12,895
Retail [Member] | Government [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	11,900	14,149
Wholesale [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	$ 2,207	$ 14