Retirement Plans and Other Postretirement Benefits - Expected Amortization Expense (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014
Retirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Amortization of net actuarial loss	$ 1,308
Accretion of prior service cost	(280)
Other Post Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Amortization of net actuarial loss	54
Accretion of prior service cost	$ 0