Derivative Instruments and Hedging Activities - Location and Fair Value Amounts of Derivative Instruments Not Qualifying as Hedging Instruments Reported in Balance Sheet (Detail) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Not Designated as Hedging Instrument [Member] | Commodity Contracts [Member] | Current Assets [Member]
Asset Derivatives
Current assets: Fair value of derivative contracts	$ 4.3	$ 12.1