Derivatives, Hedges, Financial Instruments and Carbon Credits - Realized and Unrealized Net Gains (Losses) Included in Earnings and Income Statement Classifications (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Total net gains (losses) included in earnings:
Derivative instruments and carbon credits, gains and losses recognized in earnings	$ (90)	$ (40)	$ (276)	$ (449)
Change in unrealized gains (losses) relating to contracts still held at period end:
Derivative instruments and carbon credits, change in unrealized gains and losses recognized in earnings	75	151	500	291
Cost of sales [Member] | Commodities contracts [Member]
Total net gains (losses) included in earnings:
Derivative instruments and carbon credits, gains and losses recognized in earnings		157	(275)	85
Change in unrealized gains (losses) relating to contracts still held at period end:
Derivative instruments and carbon credits, change in unrealized gains and losses recognized in earnings		171		85
Cost of sales [Member] | Foreign exchange contracts [Member]
Total net gains (losses) included in earnings:
Derivative instruments and carbon credits, gains and losses recognized in earnings		(11)		(19)
Other income [Member] | Carbon credits [Member]
Total net gains (losses) included in earnings:
Derivative instruments and carbon credits, gains and losses recognized in earnings		248	546	248
Change in unrealized gains (losses) relating to contracts still held at period end:
Derivative instruments and carbon credits, change in unrealized gains and losses recognized in earnings		184	534	184
Other expense [Member] | Contractual obligations relating to carbon credits [Member]
Total net gains (losses) included in earnings:
Derivative instruments and carbon credits, gains and losses recognized in earnings		(248)	(546)	(248)
Change in unrealized gains (losses) relating to contracts still held at period end:
Derivative instruments and carbon credits, change in unrealized gains and losses recognized in earnings		(184)	(534)	(184)
Interest expense [Member] | Interest rate contracts [Member]
Total net gains (losses) included in earnings:
Derivative instruments and carbon credits, gains and losses recognized in earnings	(90)	(186)	(1)	(515)
Change in unrealized gains (losses) relating to contracts still held at period end:
Derivative instruments and carbon credits, change in unrealized gains and losses recognized in earnings	$ 75	$ (20)	$ 500	$ 206