Disaggregation of Revenue - Schedule of Revenue Disaggregation for Customer Type (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 28, 2019	Sep. 29, 2018	Sep. 30, 2017
Disaggregation Of Revenue [Line Items]
Total revenues	$ 1,267,705	$ 1,344,413	$ 1,187,886
Retail [Member] | Residential [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	731,468	759,468	669,724
Retail [Member] | Commercial [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	333,078	354,493	306,958
Retail [Member] | Industrial [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	104,992	109,740	97,742
Retail [Member] | Agricultural [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	39,937	44,581	36,632
Retail [Member] | Government [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	53,764	56,598	47,025
Wholesale [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	$ 4,466	$ 19,533	$ 29,805