Fair Value (Derivative Assets and Liabilities by Hierarchy) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net derivative asset (liability)	$ (2,465)	$ (1,660)
Fair Value, Measurements, Recurring | Level One
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net derivative asset (liability)	0	0
Fair Value, Measurements, Recurring | Level Two
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net derivative asset (liability)	(2,465)	(1,660)
Fair Value, Measurements, Recurring | Level Three
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net derivative asset (liability)	0	0
Commodity Futures Natural Gas Contracts | Fair Value, Measurements, Recurring | Level One
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net derivative asset (liability)	0	0
Commodity Futures Natural Gas Contracts | Fair Value, Measurements, Recurring | Level Two
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net derivative asset (liability)	(2,868)	413
Commodity Futures Natural Gas Contracts | Fair Value, Measurements, Recurring | Level Three
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net derivative asset (liability)	0	0
Currency Contracts | Fair Value, Measurements, Recurring | Level One
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net derivative asset (liability)	0	0
Currency Contracts | Fair Value, Measurements, Recurring | Level Two
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net derivative asset (liability)	403	0
Currency Contracts | Fair Value, Measurements, Recurring | Level Three
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net derivative asset (liability)	0	0
Interest rate agreements | Fair Value, Measurements, Recurring | Level One
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net derivative asset (liability)	0	0
Interest rate agreements | Fair Value, Measurements, Recurring | Level Two
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net derivative asset (liability)	0	(2,073)
Interest rate agreements | Fair Value, Measurements, Recurring | Level Three
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net derivative asset (liability)	0	0
Total | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net derivative asset (liability)	(2,465)	(1,660)
Total | Commodity Futures Natural Gas Contracts | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net derivative asset (liability)	(2,868)	413
Total | Currency Contracts | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net derivative asset (liability)	403	0
Total | Interest rate agreements | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net derivative asset (liability)	$ 0	$ (2,073)