Financial Instruments and Risk Management (Fair Value of Derivative Instruments Not Designated as Hedging Instruments) (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Commodity Derivative Contracts [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives
Liability Derivatives
Commodity Derivative Contracts [Member] | Accounts Receivable [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	23,168,000	1,970,000
Foreign exchange derivative contract [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives
Liability Derivatives	25,000	26,000
Foreign exchange derivative contract [Member] | Accounts Payable [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives	$ 25,000	$ 1,038,000