Pension Plans and Other Postretirement Benefits - Estimated Amounts to Be Amortized from Accumulated Other Comprehensive Income into Net Periodic Benefit Costs (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2015
Total Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Amortization of prior service benefit	$ (95)	$ (95)	$ (95)
Total Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Amortization of prior service benefit	(677)	(689)	(757)
Domestic Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Amortization of prior service benefit	(727)	(741)	(812)
Forecast for 2013 | Total Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Amortization of prior service benefit				(95)
Forecast for 2013 | Total Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Amortization of prior service benefit				126
Forecast for 2013 | Domestic Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Amortization of prior service benefit				$ 75