Derivative Contracts - Summary of Outstanding Commodity Derivative Contracts (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Net Notional Amount	$ 8.5	$ 7.9
Notional Amount - Long [Member]
Derivatives, Fair Value [Line Items]
Net Notional Amount	40.4	24.4
Notional Amount - Short [Member]
Derivatives, Fair Value [Line Items]
Net Notional Amount	31.9	16.5
Metal [Member] | Notional Amount - Long [Member]
Derivatives, Fair Value [Line Items]
Net Notional Amount	4.1	6.7
Energy and utilities [Member] | Notional Amount - Long [Member]
Derivatives, Fair Value [Line Items]
Net Notional Amount	$ 4.4	$ 1.2