Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 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	525	(1)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	147	198
Net current-period other comprehensive income (loss)	672	197
Ending balance	(5,168)	(5,479)
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	176	165
Net current-period other comprehensive income (loss)	176	165
Ending balance	(5,404)	(5,478)
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	525	(1)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(29)	33
Net current-period other comprehensive income (loss)	496	32
Ending balance	$ 236	$ (1)