Components of Net Periodic Benefit (Income) Cost (Detail) - USD ($)	4 Months Ended
	Apr. 20, 2019	Apr. 21, 2018
Defined Benefit Plan Disclosure [Line Items]
Settlement loss	$ 0	$ 4,668,000
Pension plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	216,000	288,000
Interest cost	3,671,000	3,124,000
Expected return on plan assets	(5,276,000)	(5,407,000)
Settlement loss		4,668,000
Amortization of prior service cost (credit)	119,000	100,000
Amortization of net (gain) loss	2,184,000	1,573,000
Total net periodic pension cost (income)	914,000	4,346,000
Postretirement Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	87,000	89,000
Interest cost	91,000	72,000
Amortization of prior service cost (credit)	(13,000)	(65,000)
Amortization of net (gain) loss	(85,000)	(133,000)
Total net periodic pension cost (income)	$ 80,000	$ (37,000)