Retirement Plans - Schedule of Weighted-Average Assumptions Used to Determine Benefit Obligation (Detail) - Benefit Obligation [Member]	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net Periodic Benefit Cost Assumptions [Line Items]
Discount rate	3.74%	3.88%	3.61%
Health care cost trend: Initial	6.00%	6.25%	6.50%
Health care cost trend: Ultimate	4.75%	4.75%	4.75%
Year ultimate reached	2022	2022	2022