Other Expense, Other Income and Non-Operating Other Income, net - Schedule of Other Expense, Other Income and Non-Operating Other Income, net (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Other expense:
Losses on sales and disposals of property and equipment	$ 996	$ 1,280	$ 460
Realized and unrealized losses on contractual obligations associated with carbon credits	721	1,844	644
Miscellaneous expense	401	699	158
Total other expense	2,118	3,823	1,262
Other income:
Settlements of litigation and potential litigation	2,303	1,562
Realized and unrealized gains on carbon credits	876	1,995	644
Property insurance recoveries in excess of losses incurred			7,518
Miscellaneous income	632	381	265
Total other income	3,811	3,938	8,427
Non-operating other income, net:
Interest income	87	77	133
Miscellaneous income	263
Miscellaneous expense	(69)	(77)	(80)
Total non-operating other income, net	$ 281		$ 53