Disaggregation of Revenue - Schedule of Revenue Disaggregation for Customer Type (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 27, 2020	Jun. 29, 2019	Jun. 27, 2020	Jun. 29, 2019
Disaggregation Of Revenue [Line Items]
Total revenues	$ 206,906	$ 214,212	$ 941,839	$ 1,095,693
Retail [Member] | Residential [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	123,157	110,875	568,644	644,699
Retail [Member] | Commercial [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	53,502	65,454	232,165	280,113
Retail [Member] | Industrial [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	18,254	22,853	73,508	85,284
Retail [Member] | Agricultural [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	5,317	5,761	28,885	33,529
Retail [Member] | Government [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	6,659	8,546	38,594	47,819
Wholesale [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	$ 17	$ 723	$ 43	$ 4,249