Gross Amounts of Recognized Assets and Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Asset
Derivative assets as classified in the unaudited consolidated balance sheet	$ 0.6	$ 0.2
Derivative assets, effect of counterparty netting arrangements	0.0	(0.2)
Net derivatives assets (liabilities) as classified in the consolidated balance sheets	0.6	0.0
Liability
Derivative liabilities as classified in the unaudited consolidated balance sheet	(0.4)	(0.9)
Derivative liabilities, effect of counterparty netting arrangements	0.0	0.2
Net derivatives assets (liabilities) as classified in the consolidated balance sheets	(0.4)	(0.7)
Metal
Asset
Derivative assets as classified in the unaudited consolidated balance sheet	0.0	0.2
Liability
Derivative liabilities as classified in the unaudited consolidated balance sheet	(0.4)	(0.3)
Natural Gas
Asset
Derivative assets as classified in the unaudited consolidated balance sheet	0.6	0.0
Liability
Derivative liabilities as classified in the unaudited consolidated balance sheet	$ 0.0	$ (0.6)

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
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-Section 45
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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