Retirement Plans and Other Postretirement Benefits - Expected Amortization Expense (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($)
Retirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Amortization of net actuarial loss	$ 1,227
Accretion of prior service cost	(283)
Other Post Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Amortization of net actuarial loss	208
Accretion of prior service cost	$ 0