Employee Benefit Plans - Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 28, 2019	Sep. 29, 2018	Sep. 30, 2017
Components of net periodic benefit costs included in operating expenses [Abstract]
Settlement charge	$ 0	$ 0	$ 6,100
Pension Benefits [Member]
Components of net periodic benefit costs included in operating expenses [Abstract]
Interest cost	3,943	3,778	4,164
Expected return on plan assets	(1,723)	(1,894)	(2,150)
Amortization of prior service credit	0	0	0
Settlement charge	0	0	6,100
Recognized net actuarial loss (gain)	3,466	3,683	5,201
Net periodic benefit costs	5,686	5,567	13,315
Retiree Health and Life Benefits [Member]
Components of net periodic benefit costs included in operating expenses [Abstract]
Interest cost	275	277	385
Expected return on plan assets	0	0	0
Amortization of prior service credit	(498)	(498)	0
Settlement charge	0	0	0
Recognized net actuarial loss (gain)	(761)	(654)	(389)
Net periodic benefit costs	$ (984)	$ (875)	$ (4)