Derivatives, Hedges, Financial Instruments and Carbon Credits - Realized and Unrealized Net Losses Included in Earnings and Income Statement (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Total net gains (losses) included in earnings:
Derivative instruments and carbon credits, gains and losses recognized in earnings	$ (373)	$ (2,251)	$ (1,561)
Change in unrealized gains (losses) relating to contracts still held at year end:
Derivative instruments and carbon credits, change in unrealized gains and losses recognized in earnings	38	(335)	844
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	14	(523)	(59)
Change in unrealized gains (losses) relating to contracts still held at year end:
Derivative instruments and carbon credits, change in unrealized gains and losses recognized in earnings	79	11	761
Cost of sales [Member] | Foreign exchange contract [Member]
Total net gains (losses) included in earnings:
Derivative instruments and carbon credits, gains and losses recognized in earnings	(19)	46	25
Change in unrealized gains (losses) relating to contracts still held at year end:
Derivative instruments and carbon credits, change in unrealized gains and losses recognized in earnings			49
Other income [Member] | Carbon credits [Member]
Total net gains (losses) included in earnings:
Derivative instruments and carbon credits, gains and losses recognized in earnings	876	1,995	644
Change in unrealized gains (losses) relating to contracts still held at year end:
Derivative instruments and carbon credits, change in unrealized gains and losses recognized in earnings	78	42	644
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	(721)	(1,844)	(644)
Change in unrealized gains (losses) relating to contracts still held at year end:
Derivative instruments and carbon credits, change in unrealized gains and losses recognized in earnings	(78)	(42)	(644)
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	(523)	(1,925)	(1,527)
Change in unrealized gains (losses) relating to contracts still held at year end:
Derivative instruments and carbon credits, change in unrealized gains and losses recognized in earnings	$ (41)	$ (346)	$ 34