Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax [Roll Forward]
Beginning balance	$ (5,840)	$ (5,676)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(283)	(7)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	372	115
Net current-period other comprehensive income (loss)	89	108
Ending balance	(5,751)	(5,568)
UnrealizedGainsLossesFromDefinedBenefitPensionAndPostretirementPlanItems [Member]
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax [Roll Forward]
Beginning balance	(5,580)	(5,643)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(89)	82
Net current-period other comprehensive income (loss)	89	82
Ending balance	(5,491)	(5,561)
Accumulated (Gain) Loss from Commodity Contracts Cash Flows Hedges [Member]
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax [Roll Forward]
Beginning balance	(260)	(33)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(283)	(7)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(283)	(33)
Net current-period other comprehensive income (loss)	0	26
Ending balance	$ (260)	$ (7)