Retirement Plans (Reconciliation of Changes in Benefit Obligations, Plan Assets and Funded Status of Retirement Plans) (Details) - USD ($) $ in Thousands	4 Months Ended	12 Months Ended
	Jan. 19, 2020	Sep. 27, 2020	Sep. 29, 2019	Sep. 30, 2018
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value at beginning of year	$ 476,194	$ 476,194
Settlements	(122,300)
Fair value at end of year		365,510	$ 476,194
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position [Abstract]
Net actuarial loss (gain)		4,875	62,377	$ (31,478)
Total recognized in OCI		(39,741)	58,460	(36,466)
Supplemental Employee Retirement Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Obligation at beginning of year	79,893	79,893	73,067
Service cost		0	0	490
Interest cost		2,499	3,080	2,894
Participant contributions		0	0
Actuarial loss (gain)		1,739	8,771
Benefits paid		(5,160)	(5,025)
Settlements		0	0
Other		0	0
Obligation at end of year		78,971	79,893	73,067
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value at beginning of year	0	0	0
Actual return on plan assets		0	0
Participant contributions		0	0
Employer contributions		5,160	5,025
Benefits paid		(5,160)	(5,025)
Settlements		0	0
Other		0	0
Fair value at end of year		0	0	0
Unfunded status at end of year		(78,971)	(79,893)
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position [Abstract]
Current liabilities		(5,223)	(5,371)
Noncurrent liabilities		(73,748)	(74,522)
Total liability recognized		(78,971)	(79,893)
Unamortized actuarial loss (gain), net		34,890	34,803
Unamortized prior service cost		72	157
Total		34,962	34,960
Net actuarial loss (gain)		1,739	8,771
Pension settlement costs		0	0
Amortization of actuarial (loss) gain		(1,652)	(1,207)
Amortization of prior service cost		(85)	(115)
Total recognized in OCI		2	7,449
Net periodic benefit cost (credit) and other losses		4,236	4,402	5,068
Total recognized in comprehensive income		4,238	11,851
Net actuarial loss (gain)		1,743
Prior service cost		19
Total		1,762
Postretirement Health Plans
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Obligation at beginning of year	25,632	25,632	23,461
Service cost		0	0
Interest cost		807	997	955
Participant contributions		106	112
Actuarial loss (gain)		(4,391)	2,343
Benefits paid		(1,246)	(1,354)
Settlements		0	0
Other		57	73
Obligation at end of year		20,965	25,632	23,461
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value at beginning of year	0	0	0
Actual return on plan assets		0	0
Participant contributions		106	112
Employer contributions		1,083	1,169
Benefits paid		(1,246)	(1,354)
Settlements		0	0
Other		57	73
Fair value at end of year		0	0	0
Unfunded status at end of year		(20,965)	(25,632)
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position [Abstract]
Current liabilities		(1,243)	(1,379)
Noncurrent liabilities		(19,722)	(24,253)
Total liability recognized		(20,965)	(25,632)
Unamortized actuarial loss (gain), net		(4,174)	235
Unamortized prior service cost		0	0
Total		(4,174)	235
Net actuarial loss (gain)		(4,391)	2,343
Pension settlement costs		0	0
Amortization of actuarial (loss) gain		(18)	159
Amortization of prior service cost		0	0
Total recognized in OCI		(4,409)	2,502
Net periodic benefit cost (credit) and other losses		825	838	928
Total recognized in comprehensive income		(3,584)	3,340
Net actuarial loss (gain)		(341)
Prior service cost		0
Total		(341)
Qualified Pension Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Obligation at beginning of year	521,931	521,931	457,109
Service cost		0	0
Interest cost		13,377	19,825	19,463
Participant contributions		0	0
Actuarial loss (gain)		14,498	61,029
Benefits paid		(12,980)	(12,224)
Settlements		(124,253)	(3,808)
Other		0	0
Obligation at end of year		412,573	521,931	457,109
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value at beginning of year	$ 476,194	476,194	456,127
Actual return on plan assets		26,549	36,099
Participant contributions		0	0
Employer contributions		0	0
Benefits paid		(12,980)	(12,224)
Settlements		(124,253)	(3,808)
Other		0	0
Fair value at end of year		365,510	476,194	456,127
Unfunded status at end of year		(47,063)	(45,737)
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position [Abstract]
Current liabilities		0	0
Noncurrent liabilities		(47,063)	(45,737)
Total liability recognized		(47,063)	(45,737)
Unamortized actuarial loss (gain), net		152,370	187,705
Unamortized prior service cost		0	0
Total		152,370	187,705
Net actuarial loss (gain)		7,527	51,263
Pension settlement costs		(39,218)	0
Amortization of actuarial (loss) gain		(3,644)	(2,754)
Amortization of prior service cost		0	0
Total recognized in OCI		(35,335)	48,509
Net periodic benefit cost (credit) and other losses		36,661	(3,755)	$ (3,673)
Total recognized in comprehensive income		1,326	$ 44,754
Net actuarial loss (gain)		3,511
Prior service cost		0
Total		$ 3,511