Retirement Plans and Other Post-Retirement Benefits - Weighted-Average Assumptions Used in Computing Benefit Obligations (Detail)	Dec. 31, 2016	Dec. 31, 2015
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate - benefit obligation	4.43%	4.65%
Future compensation growth rate	3.00%	3.50%
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate - benefit obligation	4.18%	4.38%