Gross Amounts of Recognized Assets and Liabilities (Detail) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Asset
Derivative assets as classified in the unaudited consolidated balance sheet	$ 0.4	$ 0.6
Derivative assets, effect of counterparty netting arrangements	0.0	0.0
Net derivative assets (liabilities) as classified in the condensed consolidated balance sheets	0.4	0.6
Liability
Derivative liabilities as classified in the unaudited condensed consolidated balance sheet	(0.3)	(0.4)
Derivative liabilities, effect of counterparty netting arrangements	0.0	0.0
Net derivative assets (liabilities) as classified in the condensed consolidated balance sheets	(0.3)	(0.4)
Metal
Asset
Derivative assets as classified in the unaudited consolidated balance sheet	0.0	0.0
Liability
Derivative liabilities as classified in the unaudited condensed consolidated balance sheet	(0.3)	(0.4)
Natural Gas
Asset
Derivative assets as classified in the unaudited consolidated balance sheet	0.4	0.6
Liability
Derivative liabilities as classified in the unaudited condensed consolidated balance sheet	$ 0.0	$ 0.0

Amount of obligation to return cash collateral under master netting arrangements offset against derivative assets.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

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

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