Employee Benefit Plans - Amounts recognized in balance sheet (Details) - USD ($)	Nov. 29, 2020	Nov. 24, 2019
Pension plans, defined benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets for Plan Benefits, Defined Benefit Plan	$ 62,161,000	$ 27,704,000
Accrued benefit liability – current portion	(9,663,000)	(9,480,000)
Accrued benefit liability – long-term portion	(163,836,000)	(188,825,000)
Amount recognized in balance sheet	(111,338,000)	(170,601,000)
Accumulated other comprehensive loss:
Net actuarial loss	(296,330,000)	(358,484,000)
Net prior service benefit	259,000	291,000
Other comprehensive income (loss)	(296,071,000)	(358,193,000)
Other postretirement benefit plans, defined benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets for Plan Benefits, Defined Benefit Plan	0	0
Accrued benefit liability – current portion	(7,112,000)	(8,129,000)
Accrued benefit liability – long-term portion	(60,249,000)	(64,006,000)
Amount recognized in balance sheet	(67,361,000)	(72,135,000)
Accumulated other comprehensive loss:
Net actuarial loss	(12,491,000)	(11,284,000)
Net prior service benefit	0	0
Other comprehensive income (loss)	$ (12,491,000)	$ (11,284,000)