Derivatives, Hedges, Financial Instruments and Carbon Credits - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (Recurring [Member], USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Assets - Supplies, prepaid items and other:
Total	$ 2,779	$ 1,315
Liabilities - Current and noncurrent accrued and other liabilities:
Total	5,934	2,524
Commodities Contracts [Member]
Assets - Supplies, prepaid items and other:
Derivative Assets		31
Liabilities - Current and noncurrent accrued and other liabilities:
Derivative Financial Instruments, Liabilities	2,440
Carbon Credits [Member]
Assets - Supplies, prepaid items and other:
Carbon credits	2,779	1,284
Liabilities - Current and noncurrent accrued and other liabilities:
Contractual obligations - carbon credits	2,779	1,284
Interest Rate Contracts [Member]
Liabilities - Current and noncurrent accrued and other liabilities:
Derivative Financial Instruments, Liabilities	671	1,240
Foreign Exchange Contracts [Member]
Liabilities - Current and noncurrent accrued and other liabilities:
Derivative Financial Instruments, Liabilities	44
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Liabilities - Current and noncurrent accrued and other liabilities:
Total	316
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Commodities Contracts [Member]
Liabilities - Current and noncurrent accrued and other liabilities:
Derivative Financial Instruments, Liabilities	316
Significant Other Observable Inputs (Level 2) [Member]
Liabilities - Current and noncurrent accrued and other liabilities:
Total	2,839
Significant Other Observable Inputs (Level 2) [Member] | Commodities Contracts [Member]
Liabilities - Current and noncurrent accrued and other liabilities:
Derivative Financial Instruments, Liabilities	2,124
Significant Other Observable Inputs (Level 2) [Member] | Interest Rate Contracts [Member]
Liabilities - Current and noncurrent accrued and other liabilities:
Derivative Financial Instruments, Liabilities	671
Significant Other Observable Inputs (Level 2) [Member] | Foreign Exchange Contracts [Member]
Liabilities - Current and noncurrent accrued and other liabilities:
Derivative Financial Instruments, Liabilities	44
Significant Unobservable Inputs (Level 3) [Member]
Assets - Supplies, prepaid items and other:
Total	2,779
Liabilities - Current and noncurrent accrued and other liabilities:
Total	2,779
Significant Unobservable Inputs (Level 3) [Member] | Carbon Credits [Member]
Assets - Supplies, prepaid items and other:
Carbon credits	2,779
Liabilities - Current and noncurrent accrued and other liabilities:
Contractual obligations - carbon credits	$ 2,779