Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands		4 Months Ended
		Apr. 21, 2018	Apr. 22, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net income		$ 51,247	$ 60,418
Pension and postretirement plans:
Settlement loss		3,490
Net gain for the period		8,813
Amortization of prior service cost included in net income		26	33
Amortization of actuarial loss included in net income		1,076	1,110
Pension and postretirement plans, net of tax		13,405	1,143
Derivative instruments:
Net change in fair value of derivatives	[1]	10,470	(3,518)
Loss reclassified to net income		297	474
Derivative instruments, net of tax		10,767	(3,044)
Other comprehensive income (loss), net of tax		24,172	(1,901)
Comprehensive income		$ 75,419	$ 58,517

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