Disaggregation of Revenue - Schedule of Revenue Disaggregation for Customer Type (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 29, 2018	Dec. 30, 2017
Disaggregation Of Revenue [Line Items]
Total revenues	$ 377,104	$ 373,277
Retail [Member] | Residential [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	221,714	214,208
Retail [Member] | Commercial [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	96,578	93,942
Retail [Member] | Industrial [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	29,191	28,631
Retail [Member] | Agricultural [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	13,664	15,492
Retail [Member] | Government [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	15,934	15,126
Wholesale [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	$ 23	$ 5,878