AOCI Related to Derivative Transactions (Detail) - USD ($) $ in Thousands		4 Months Ended
		Apr. 20, 2019	Apr. 21, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Net change in fair value of derivatives	[1]	$ (9,593)	$ 10,470
Closed Contracts
Derivative Instruments, Gain (Loss) [Line Items]
Estimated amount of derivatives to be reclassified in income from AOCI		1,038
Closed Contracts | Commodity price risk derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Estimated amount of derivatives to be reclassified in income from AOCI		990
Closed Contracts | Interest rate risk derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Estimated amount of derivatives to be reclassified in income from AOCI		48
Expiring in 2019
Derivative Instruments, Gain (Loss) [Line Items]
Net change in fair value of derivatives		(14,036)
Expiring in 2019 | Commodity price risk derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Net change in fair value of derivatives		(14,036)
Expiring in 2020
Derivative Instruments, Gain (Loss) [Line Items]
Net change in fair value of derivatives		(2,854)
Expiring in 2020 | Commodity price risk derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Net change in fair value of derivatives		(2,854)
Expiring in 2021
Derivative Instruments, Gain (Loss) [Line Items]
Net change in fair value of derivatives		(54)
Expiring in 2021 | Commodity price risk derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Net change in fair value of derivatives		(54)
Closed or Expiring Over Next Four Years
Derivative Instruments, Gain (Loss) [Line Items]
Net change in fair value of derivatives		(15,906)
Closed or Expiring Over Next Four Years | Commodity price risk derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Net change in fair value of derivatives		(15,954)
Closed or Expiring Over Next Four Years | Interest rate risk derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Net change in fair value of derivatives		$ 48

[1] Amounts in parentheses indicate debits to determine net income (loss).