Derivatives, Hedges, Financial Instruments and Carbon Credits - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - Recurring [Member] - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Assets - Supplies, prepaid items and other:
Total	$ 190	$ 2,779
Liabilities - Current and noncurrent accrued and other liabilities:
Total	1,380	5,934
Commodities Contracts [Member]
Liabilities - Current and noncurrent accrued and other liabilities:
Derivative Financial Instruments, Liabilities	915	2,440
Carbon Credits [Member]
Assets - Supplies, prepaid items and other:
Carbon credits	187	2,779
Liabilities - Current and noncurrent accrued and other liabilities:
Contractual obligations - carbon credits	187	2,779
Interest Rate Contracts [Member]
Liabilities - Current and noncurrent accrued and other liabilities:
Derivative Financial Instruments, Liabilities	278	671
Foreign Exchange Contracts [Member]
Assets - Supplies, prepaid items and other:
Foreign exchange contracts	3
Liabilities - Current and noncurrent accrued and other liabilities:
Derivative Financial Instruments, Liabilities		$ 44
Significant Other Observable Inputs (Level 2) [Member]
Assets - Supplies, prepaid items and other:
Total	3
Liabilities - Current and noncurrent accrued and other liabilities:
Total	1,193
Significant Other Observable Inputs (Level 2) [Member] | Commodities Contracts [Member]
Liabilities - Current and noncurrent accrued and other liabilities:
Derivative Financial Instruments, Liabilities	915
Significant Other Observable Inputs (Level 2) [Member] | Interest Rate Contracts [Member]
Liabilities - Current and noncurrent accrued and other liabilities:
Derivative Financial Instruments, Liabilities	278
Significant Other Observable Inputs (Level 2) [Member] | Foreign Exchange Contracts [Member]
Assets - Supplies, prepaid items and other:
Foreign exchange contracts	3
Significant Unobservable Inputs (Level 3) [Member]
Assets - Supplies, prepaid items and other:
Total	187
Liabilities - Current and noncurrent accrued and other liabilities:
Total	187
Significant Unobservable Inputs (Level 3) [Member] | Carbon Credits [Member]
Assets - Supplies, prepaid items and other:
Carbon credits	187
Liabilities - Current and noncurrent accrued and other liabilities:
Contractual obligations - carbon credits	$ 187