Disaggregation of Revenue - Schedule of Revenue Disaggregation for Customer Type (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 27, 2021	Mar. 28, 2020	Mar. 27, 2021	Mar. 28, 2020
Disaggregation Of Revenue [Line Items]
Total revenues	$ 537,238	$ 401,055	$ 842,429	$ 734,933
Retail [Member] | Residential [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	310,930	248,601	485,641	445,487
Retail [Member] | Commercial [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	128,886	95,328	208,326	178,663
Retail [Member] | Industrial [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	35,447	28,655	61,242	55,254
Retail [Member] | Agricultural [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	13,571	10,673	24,709	23,568
Retail [Member] | Government [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	23,572	17,787	35,472	31,935
Wholesale [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	$ 24,832	$ 12	$ 27,039	$ 26