Derivatives (Fair Value of Derivative Assets and Liabilities) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Derivatives, Fair Value [Line Items]
Fair value, derivative asset	$ 578	$ 413
Fair value, derivative liability	1,644	2,073
Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Fair value, derivative asset	578	413
Fair value, derivative liability	1,537	1,866
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Fair value, derivative liability	107	207
Interest rate agreements [Member] | Designated as Hedging Instrument [Member] | Derivative Liability, Current [Member]
Derivatives, Fair Value [Line Items]
Fair value, derivative liability	1,537	0
Interest rate agreements [Member] | Designated as Hedging Instrument [Member] | Other Long-Term Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value, derivative liability	0	1,866
Interest rate agreements [Member] | Not Designated as Hedging Instrument [Member] | Derivative Liability, Current [Member]
Derivatives, Fair Value [Line Items]
Fair value, derivative liability	107	0
Interest rate agreements [Member] | Not Designated as Hedging Instrument [Member] | Other Long-Term Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value, derivative liability	0	207
Natural gas contracts [Member] | Designated as Hedging Instrument [Member] | Prepaid and other current assets [Member]
Derivatives, Fair Value [Line Items]
Fair value, derivative asset	573	394
Natural gas contracts [Member] | Designated as Hedging Instrument [Member] | Derivative Asset [Member]
Derivatives, Fair Value [Line Items]
Fair value, derivative asset	$ 5	$ 19