Defined Benefit Pension And Other Postretirement Plans (Multi Employer Pension Plan) (Detail) - Multiemployer Plans, Pension	12 Months Ended
	Dec. 31, 2016 USD ($) Employee		Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Multiemployer Plans [Line Items]
Multiemployer pension plan, minimum contribution requirement per week per employee	$ 303
Number of employees participated in the plan | Employee	280
Central States, Southeast and Southwest Pension Plan [Member]
Multiemployer Plans [Line Items]
MPC contributions	$ 4,000,000	[1]	$ 4,000,000	$ 4,000,000

[1] This agreement has a minimum contribution requirement of $303 per week per employee for 2017. A total of 280 employees participated in the plan as of December 31, 2016.