Derivative Financial Instruments (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended 9 Months Ended 9 Months Ended 3 Months Ended 9 Months Ended 3 Months Ended 9 Months Ended
Sep. 30, 2012
Derivatives in Cash Flow Hedging Relationships [Member]
Sep. 30, 2011
Derivatives in Cash Flow Hedging Relationships [Member]
Sep. 30, 2012
Derivatives in Cash Flow Hedging Relationships [Member]
Sep. 30, 2011
Derivatives in Cash Flow Hedging Relationships [Member]
Sep. 30, 2012
Designated as Hedging Instrument [Member]
Dec. 31, 2011
Designated as Hedging Instrument [Member]
Sep. 30, 2012
Commodity Contract [Member]
MMBTU
Dec. 31, 2011
Commodity Contract [Member]
MMBTU
Sep. 30, 2012
Commodity Contract [Member]
Derivatives in Cash Flow Hedging Relationships [Member]
Product Cost [Member]
Sep. 30, 2011
Commodity Contract [Member]
Derivatives in Cash Flow Hedging Relationships [Member]
Product Cost [Member]
Sep. 30, 2012
Commodity Contract [Member]
Derivatives in Cash Flow Hedging Relationships [Member]
Product Cost [Member]
Sep. 30, 2011
Commodity Contract [Member]
Derivatives in Cash Flow Hedging Relationships [Member]
Product Cost [Member]
Sep. 30, 2012
Commodity Contract [Member]
Designated as Hedging Instrument [Member]
Other Current Assets [Member]
Dec. 31, 2011
Commodity Contract [Member]
Designated as Hedging Instrument [Member]
Other Current Assets [Member]
Sep. 30, 2012
Commodity Contract [Member]
Designated as Hedging Instrument [Member]
Other Assets [Member]
Dec. 31, 2011
Commodity Contract [Member]
Designated as Hedging Instrument [Member]
Other Assets [Member]
Sep. 30, 2012
Commodity Contract [Member]
Designated as Hedging Instrument [Member]
Accrued Expenses [Member]
Dec. 31, 2011
Commodity Contract [Member]
Designated as Hedging Instrument [Member]
Accrued Expenses [Member]
Sep. 30, 2012
Commodity Contract [Member]
Designated as Hedging Instrument [Member]
Other Noncurrent Liabilities [Member]
Dec. 31, 2011
Commodity Contract [Member]
Designated as Hedging Instrument [Member]
Other Noncurrent Liabilities [Member]
Sep. 30, 2011
Interest Rate Swap [Member]
Derivatives in Cash Flow Hedging Relationships [Member]
Interest Expense [Member]
Sep. 30, 2011
Interest Rate Swap [Member]
Derivatives in Cash Flow Hedging Relationships [Member]
Interest Expense [Member]
Derivatives, Fair Value [Line Items]                                            
Underlying risk             change in natural gas prices                              
Period through which natural gas is hedged             September 2014                              
Percent of forecasted usage to be hedged (in hundredths)             90.00%                              
Maximum period which the Company hedges in advance of forecasted purchase (in months)             36 months                              
Notional amount (in MMBtus)             2.0 2.9                            
Net loss to be reclassified from accumulated other comprehensive income to earnings during the next 12 months             $ 1.3                              
Asset Derivatives         0.5 [1] 0.3 [2]             0.5 [1],[3] 0.3 [2],[4] 0 [1] 0 [2]            
Liability Derivatives         2.0 [1] 5.9 [2]                     1.8 [1],[3] 5.0 [2],[4] 0.2 [1] 0.9 [2]    
Number of counterparties             3 3                            
Number of counterparties for amounts recorded as liabilities             1 1                            
Number of counterparties for amounts recorded as assets             1 2                            
Netting of contracts in a receivable position against contracts in payable position             0.1 0.3                            
Derivative Instruments, Gain (Loss) [Line Items]                                            
Amount of (Gain) Loss Recognized in OCI on Derivative (Effective Portion) (0.6) 2.0 1.0 2.0         (0.6) 2.0 1.0 2.0                 0 0
Amount of Gain (Loss) Reclassified from Accumulated OCI Into Income (Effective Portion) $ (1.3) $ (1.9) $ (4.9) $ (4.7)         $ (1.3) $ (1.9) $ (4.9) $ (4.1)                 $ 0 $ (0.6)
[1] As of September 30, 2012, the Company has commodity hedge agreements with three counterparties. All of the amounts recorded as liabilities for the Company's commodity contracts are almost entirely payable to one counterparty. The amount recorded as an asset is due from one counterparty.
[2] The Company has commodity hedge agreements with three counterparties. All of the amounts recorded as liabilities for the Company's commodity contracts are payable almost entirely to one counterparty. The amount recorded as an asset is due from two counterparties.
[3] The Company has master netting agreements with its counterparties and accordingly has netted approximately $0.1 million of its commodity contracts that are in a receivable position against its contracts in payable positions.
[4] The Company has master netting agreements with its counterparties and accordingly has netted in its consolidated balance sheets approximately $0.3 million of its commodity contracts that are in a receivable position against its contracts in payable positions.