Fair Value of Derivative Financial Instruments (Detail) $ in Millions	Sep. 30, 2015 USD ($)
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Fair value of derivative liabilities	$ 0.8
Accrued Liabilities \| Metal
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Fair value of derivative liabilities	0.5
Accrued Liabilities \| Natural Gas
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Fair value of derivative liabilities	$ 0.3

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 55

-Paragraph 10

-URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226008-175313

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

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-Section 50

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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Reference 5: http://www.xbrl.org/2003/role/presentationRef

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-Name Accounting Standards Codification

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-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant