Disaggregation of Revenue - Schedule of Revenue Disaggregation for Customer Type (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 28, 2019	Dec. 29, 2018
Disaggregation Of Revenue [Line Items]
Total revenues	$ 333,878	$ 377,104
Retail [Member] | Residential [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	196,886	221,714
Retail [Member] | Commercial [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	83,335	96,578
Retail [Member] | Industrial [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	26,599	28,954
Retail [Member] | Agricultural [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	12,895	13,901
Retail [Member] | Government [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	14,149	15,934
Wholesale [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	$ 14	$ 23