Disaggregation of Revenue - Schedule of Revenue Disaggregation for Customer Type (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 29, 2019	Jun. 30, 2018	Jun. 29, 2019	Jun. 30, 2018
Disaggregation Of Revenue [Line Items]
Total revenues	$ 214,212	$ 241,936	$ 1,095,693	$ 1,151,495
Retail [Member] | Residential [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	110,875	128,607	644,699	665,860
Retail [Member] | Commercial [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	65,454	72,747	280,113	292,286
Retail [Member] | Industrial [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	22,853	23,835	85,284	86,864
Retail [Member] | Agricultural [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	5,761	6,798	33,529	37,199
Retail [Member] | Government [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	8,546	9,931	47,819	49,774
Wholesale [Member]
Disaggregation Of Revenue [Line Items]
Total revenues	$ 723	$ 18	$ 4,249	$ 19,512