Derivatives (Fair Value of Derivative Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Fair value, derivative asset	$ 245	$ 403
Fair value, derivative liability	4,580	2,868
Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Fair value, derivative liability	3,481	1,325
Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Fair value, derivative asset	245	403
Fair value, derivative liability	1,099	1,543
Interest Rate Agreements | Designated as Hedging Instrument | Derivative Liability - Current
Derivatives, Fair Value [Line Items]
Fair value, derivative liability	2,132	0
Interest Rate Agreements | Designated as Hedging Instrument | Other Long-Term Liabilities
Derivatives, Fair Value [Line Items]
Fair value, derivative liability	246	0
Natural Gas Contracts | Designated as Hedging Instrument | Derivative Liability - Current
Derivatives, Fair Value [Line Items]
Fair value, derivative liability	1,069	1,222
Natural Gas Contracts | Designated as Hedging Instrument | Other Long-Term Liabilities
Derivatives, Fair Value [Line Items]
Fair value, derivative liability	34	103
Natural Gas Contracts | Not Designated as Hedging Instrument | Derivative Liability - Current
Derivatives, Fair Value [Line Items]
Fair value, derivative liability	1,064	1,431
Natural Gas Contracts | Not Designated as Hedging Instrument | Other Long-Term Liabilities
Derivatives, Fair Value [Line Items]
Fair value, derivative liability	35	112
Currency Contracts | Not Designated as Hedging Instrument | Prepaid and other current assets
Derivatives, Fair Value [Line Items]
Fair value, derivative asset	$ 245	$ 403