Derivatives (Fair Value of Derivative Assets and Liabilities) (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Derivatives, Fair Value [Line Items]
Fair value, derivative asset	$ 88	$ 245
Fair value, derivative liability	6,334	4,580
Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Fair value, derivative asset	46	0
Fair value, derivative liability	6,189	3,481
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Fair value, derivative asset	42	245
Fair value, derivative liability	145	1,099
Currency contracts [Member] | Not Designated as Hedging Instrument [Member] | Prepaid and other current assets [Member]
Derivatives, Fair Value [Line Items]
Fair value, derivative asset	0	245
Currency contracts [Member] | Not Designated as Hedging Instrument [Member] | Derivative Liability, Current [Member]
Derivatives, Fair Value [Line Items]
Fair value, derivative liability	143	0
Natural Gas Contracts | Designated as Hedging Instrument [Member] | Prepaid and other current assets [Member]
Derivatives, Fair Value [Line Items]
Fair value, derivative asset	45	0
Natural Gas Contracts | Designated as Hedging Instrument [Member] | Other Assets [Member]
Derivatives, Fair Value [Line Items]
Fair value, derivative asset	1	0
Natural Gas Contracts | Designated as Hedging Instrument [Member] | Derivative Liability, Current [Member]
Derivatives, Fair Value [Line Items]
Fair value, derivative liability	0	1,069
Natural Gas Contracts | Designated as Hedging Instrument [Member] | Other Long-Term Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value, derivative liability	0	34
Natural Gas Contracts | Not Designated as Hedging Instrument [Member] | Prepaid and other current assets [Member]
Derivatives, Fair Value [Line Items]
Fair value, derivative asset	42	0
Natural Gas Contracts | Not Designated as Hedging Instrument [Member] | Derivative Liability, Current [Member]
Derivatives, Fair Value [Line Items]
Fair value, derivative liability	0	1,064
Natural Gas Contracts | Not Designated as Hedging Instrument [Member] | Other Long-Term Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value, derivative liability	2	35
Interest Rate Contract [Member] | Designated as Hedging Instrument [Member] | Derivative Liability, Current [Member]
Derivatives, Fair Value [Line Items]
Fair value, derivative liability	2,386	2,132
Interest Rate Contract [Member] | Designated as Hedging Instrument [Member] | Other Long-Term Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value, derivative liability	$ 3,803	$ 246