Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive Loss (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	$ (7)	$ 0
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax [Roll Forward]
Beginning balance	(5,676)	(2,533)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	115	31
Net current-period other comprehensive income (loss)	108	31
Ending balance	(5,568)	(2,502)
UnrealizedGainsLossesFromDefinedBenefitPensionAndPostretirementPlanItems [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	0
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax [Roll Forward]
Beginning balance	(5,643)	(2,533)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	82	31
Net current-period other comprehensive income (loss)	82	31
Ending balance	(5,561)	(2,502)
Accumulated (Gain) Loss from Commodity Contracts Cash Flows Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(7)	0
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax [Roll Forward]
Beginning balance	(33)	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	33	0
Net current-period other comprehensive income (loss)	26	0
Ending balance	$ (7)	$ 0