Note 8 - Postretirement and Postemployment Benefits (Details Textual) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 27, 2020	Sep. 27, 2020	Sep. 29, 2019	Sep. 30, 2018
Postretirement Health Coverage [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Curtailment			$ 2,031,000
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Curtailment				$ (7,036,000)
Other Comprehensive Income (Loss), Defined Benefit Plan, Settlement and Curtailment Gain (Loss), before Tax			(106,000)
Assets for Plan Benefits, Defined Benefit Plan		$ 15,912,000	$ 14,338,000
Postretirement Health Coverage [Member] | Forecast [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Curtailment	$ 23,800,000
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan, Expected Amortization of Gain (Loss), Next Fiscal Year		687,000
Defined Benefit Plan, Expected Amortization of Prior Service Cost (Credit), Next Fiscal Year		$ 647,000
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets		4.50%	4.50%	4.50%
Assets for Plan Benefits, Defined Benefit Plan		$ 15,241,000	$ 12,383,000
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year		0
Defined Benefit Plan, Benefit Obligation, Ending Balance		47,637,000	11,752,000	$ 11,756,000
Other Postretirement Benefits Plan [Member] | U.S. Small Cap Value Equity Common/Collective Fund [Member]
Equity Securities, FV-NI		590,000	778,000
Other Postretirement Benefits Plan [Member] | Global Equity Long/Short Common/Collective Hedge Fund-of-funds [Member]
Equity Securities, FV-NI		2,754,000	3,587,000
Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Assets Transferred into (out of) Level 3		0	0
Master Trust Assets for the Retiree Medical Plan [Member]
Assets for Plan Benefits, Defined Benefit Plan		671,000	1,955,000
Postemployment Retirement Benefits [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Curtailment		(0)	(0)	$ 2,031,000
Defined Benefit Plan, Benefit Obligation, Ending Balance		$ 2,371,000	$ 2,550,000