Stockholder's Equity - Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ (6,713)	$ (4,272)	$ (6,713)	$ (4,272)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax			1,000	(1,440)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax			81	901
Net current-period other comprehensive income (loss)			1,081	(539)
Tax Cuts and Jobs Act, Reclassification from AOCI to Retained Earnings, Tax Effect		0
Ending balance			(5,747)	(5,718)
UnrealizedGainsLossesFromDefinedBenefitPensionAndPostretirementPlanItems [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(5,928)	(4,743)	(5,928)	(4,743)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax			0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax			213	189
Net current-period other comprehensive income (loss)			213	189
Tax Cuts and Jobs Act, Reclassification from AOCI to Retained Earnings, Tax Effect				(1,022)
Ending balance			(5,715)	(5,576)
Accumulated (Gain) Loss from Commodity Contracts Cash Flows Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(785)	471	(785)	471
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax			1,000	(1,440)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax			(132)	712
Net current-period other comprehensive income (loss)			868	(728)
Prior Period Reclassification Adjustment			(115)
Tax Cuts and Jobs Act, Reclassification from AOCI to Retained Earnings, Tax Effect				115
Ending balance			(32)	(142)
AOCI Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Prior Period Reclassification Adjustment	$ (115)		$ (115)
Tax Cuts and Jobs Act, Reclassification from AOCI to Retained Earnings, Tax Effect		$ (907)		$ (907)

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Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

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Amount after tax, before reclassification adjustments of other comprehensive income (loss).

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