Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax [Roll Forward]
Beginning balance	$ (5,676)	$ (2,533)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(1)	(1)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	198	61
Net current-period other comprehensive income (loss)	197	60
Ending balance	(5,479)	(2,473)
UnrealizedGainsLossesFromDefinedBenefitPensionAndPostretirementPlanItems [Member]
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax [Roll Forward]
Beginning balance	(5,643)	(2,533)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	165	61
Net current-period other comprehensive income (loss)	165	61
Ending balance	(5,478)	(2,472)
Accumulated (Gain) Loss from Commodity Contracts Cash Flows Hedges [Member]
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax [Roll Forward]
Beginning balance	(33)	0
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(1)	(1)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	33	0
Net current-period other comprehensive income (loss)	32	(1)
Ending balance	$ (1)	$ (1)