Disaggregation of Revenue - Schedule of Revenue Disaggregation for Customer Type (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 28, 2020	Mar. 30, 2019	Mar. 28, 2020	Mar. 30, 2019
Disaggregation Of Revenue [Line Items]
Total revenues	$ 401,055	$ 504,377	$ 734,933	$ 881,481
Retail [Member] | Residential [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	248,601	312,110	445,487	533,824
Retail [Member] | Commercial [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	95,328	118,081	178,663	214,659
Retail [Member] | Industrial [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	28,655	33,477	55,254	62,431
Retail [Member] | Agricultural [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	10,673	13,867	23,568	27,768
Retail [Member] | Government [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	17,787	23,339	31,935	39,273
Wholesale [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	$ 12	$ 3,503	$ 26	$ 3,526