Postretirement Plans - Additional Information (Detail) - USD ($)			3 Months Ended			4 Months Ended	6 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jul. 14, 2018	Oct. 07, 2017	Jul. 15, 2017	Apr. 21, 2018	Jul. 14, 2018	Jul. 15, 2017	Dec. 30, 2017
Compensation And Retirement Disclosure [Abstract]
Expected long-term rate of return on plan assets	5.20%	6.40%
Voluntarily contributions made by an employer			$ 30,000,000			$ 10,000,000
Total cost and employer contributions			6,200,000		$ 6,600,000		$ 13,500,000	$ 15,600,000
Multiemployer plan, withdrawal obligation				$ 15,200,000					$ 15,223,000
Multiemployer plans, increase in withdrawal obligation						2,300,000
Multiemployer plans transition payments payable			$ 3,100,000				$ 3,100,000
Multiemployer plans payable date							Nov. 03, 2017
Multiemployer plan withdrawal liability of net present value monthly payments period				20 years
Multiemployer plan, withdrawal obligation paid						$ 200,000