Retirement Plans and Other Post-Retirement Benefits - Benefit Payments Expected to be Made under Non-Qualified Pension Plans and Other Benefit Plans (Detail) $ in Thousands	Dec. 31, 2016 USD ($)
Nonqualified Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit payments expected	$ 1,991
Other Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit payments expected	$ 3,212