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		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Total net gain (losses) included in earnings	$ (55)	$ (142)	$ (2,157)	$ 2,345
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	(70)	(105)	(2,048)	2,111
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	29		(64)
Other Income [Member] | Carbon Credits [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net gain (losses) included in earnings	1,771		1,741	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	(1,771)		(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	$ (14)	$ (37)	$ (45)	$ (57)