Derivatives, Hedges, Financial Instruments and Carbon Credits - Net Gains (Losses) Included in Earnings and the Income Statement Classifications (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Total net gain (losses) included in earnings	$ (630)	$ (200)	$ (2,787)	$ 2,145
Cost of Sales [Member] | Commodities Contracts [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net gain (losses) included in earnings	(1,526)	(214)	(3,574)	1,897
Cost of Sales [Member] | Foreign Exchange Contracts [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net gain (losses) included in earnings	2		(62)
Other Income [Member] | Carbon Credits [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net gain (losses) included in earnings	904		2,645	1,925
Other Expense [Member] | Contractual Obligations Relating to Carbon Credits [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net gain (losses) included in earnings			(1,741)	(1,634)
Interest Expense [Member] | Interest Rate Contracts [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net gain (losses) included in earnings	$ (10)	$ 14	$ (55)	$ (43)