Derivatives (Fair Value of Derivative Assets and Liabilities) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Derivatives, Fair Value [Line Items]
Fair value, derivative asset	$ 46	$ 3,713
Fair value, derivative liability	2,199	3,688
Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Fair value, derivative asset	10	3,606
Fair value, derivative liability	2,199	3,688
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Fair value, derivative asset	36	107
Fair value, derivative liability	0	0
Interest rate contracts [Member] | Designated as Hedging Instrument [Member] | Derivative Asset [Member]
Derivatives, Fair Value [Line Items]
Fair value, derivative asset	0	3,606
Interest rate contracts [Member] | Designated as Hedging Instrument [Member] | Other Long-Term Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value, derivative liability	188	0
Natural gas contracts [Member] | Designated as Hedging Instrument [Member] | Derivative Asset [Member]
Derivatives, Fair Value [Line Items]
Fair value, derivative asset	10	0
Natural gas contracts [Member] | Designated as Hedging Instrument [Member] | Derivative Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value, derivative liability	2,011	3,390
Natural gas contracts [Member] | Designated as Hedging Instrument [Member] | Other Long-Term Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value, derivative liability	0	298
Currency contracts [Member] | Not Designated as Hedging Instrument [Member] | Prepaid and Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Fair value, derivative asset	$ 36	$ 107