Disaggregation of Revenue - Schedule of Revenue Disaggregation for Customer Type (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 30, 2019	Mar. 31, 2018	Mar. 30, 2019	Mar. 31, 2018
Disaggregation Of Revenue [Line Items]
Total revenues	$ 504,377	$ 536,282	$ 881,481	$ 909,559
Retail [Member] | Residential [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	312,110	323,045	533,824	537,253
Retail [Member] | Commercial [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	118,081	125,597	214,659	219,539
Retail [Member] | Industrial [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	33,477	34,906	62,431	63,029
Retail [Member] | Agricultural [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	13,867	14,400	27,768	30,401
Retail [Member] | Government [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	23,339	24,717	39,273	39,843
Wholesale [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	$ 3,503	$ 13,616	$ 3,526	$ 19,494