Restructuring and Impairment Charges - Summary of Impairment and Restructuring Charges (Detail) $ in Thousands	3 Months Ended
Mar. 31, 2016 USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment charges	$ 1,505
Reserve beginning balance	2,290
Charges	1,559
Paid in 2016	(952)
Reserve ending balance	2,897
Severance and Other Employee Costs [Member]
Restructuring Cost and Reserve [Line Items]
Reserve beginning balance	445
Charges	815
Paid in 2016	(399)
Reserve ending balance	861
Site Closure and Other Associated Cost [Member]
Restructuring Cost and Reserve [Line Items]
Reserve beginning balance	1,845
Charges	744
Paid in 2016	(553)
Reserve ending balance	2,036
Wheeling Plant [Member]
Restructuring Cost and Reserve [Line Items]
Impairment of tangible assets	33
Restructuring charges	1,526
Restructuring and impairment charges	$ 1,559

Amount of cash payments made as the result of exit or disposal activities. Excludes payments associated with a discontinued operation or an asset retirement obligation.

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Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3602-108585

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-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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-Publisher FASB
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Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Staff Accounting Bulletin (SAB)
-Number Topic 5
-Section P
-Subsection 3, 4

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No definition available.

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Amount, after cash payment, of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation.

+ References

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Amount, after cash payment, of expenses associated with exit or disposal activities pursuant to an authorized plan and expenses resulting from the write-down of assets. Excludes expenses related to a business combination, a discontinued operation or an asset retirement obligation.

+ References

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Carrying amount (including both current and noncurrent portions of the accrual) as of the balance sheet date pertaining to a specified type of cost associated with exit from or disposal of business activities or restructuring pursuant to a duly authorized plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 420
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SAB TOPIC 5.P.4(b))
-URI http://asc.fasb.org/extlink&oid=27011515&loc=d3e140904-122747

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-Publisher SEC
-Name Staff Accounting Bulletin (SAB)
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The charge against earnings resulting from the aggregate write down of tangible assets from their carrying value to their fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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