Employee Benefit Plans - Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 25, 2021	Sep. 26, 2020	Sep. 28, 2019
Components of net periodic benefit costs included in operating expenses [Abstract]
Settlement charge	$ 958	$ 1,051	$ 0
Pension Benefits [Member]
Components of net periodic benefit costs included in operating expenses [Abstract]
Interest cost	2,263	2,726	3,943
Expected return on plan assets	(1,266)	(1,270)	(1,723)
Amortization of prior service credit	0	0	0
Settlement charge	958	1,051	0
Recognized net actuarial loss (gain)	3,289	3,448	3,466
Net periodic benefit costs	5,244	5,955	5,686
Retiree Health and Life Benefits [Member]
Components of net periodic benefit costs included in operating expenses [Abstract]
Interest cost	77	151	275
Expected return on plan assets	0	0	0
Amortization of prior service credit	(498)	(498)	(498)
Settlement charge	0	0	0
Recognized net actuarial loss (gain)	(723)	(786)	(761)
Net periodic benefit costs	$ (1,144)	$ (1,133)	$ (984)