Financial Instruments and Risk Management (Carrying Value of Assets and Liabilities Recorded at Fair Value on Recurring Basis) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Commodity Derivative Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	$ 6,200
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative liabilities	14,168	14,305
Fair Value, Measurements, Recurring [Member] | Nonqualified employee savings plans [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative liabilities	13,979	13,267
Fair Value, Measurements, Recurring [Member] | Foreign exchange derivative contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative liabilities	189	1,038
Fair Value, Measurements, Recurring [Member] | Commodity Derivative Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	6,152	1,970
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative liabilities	13,979	13,267
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair Value, Measurements, Recurring [Member] | Nonqualified employee savings plans [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative liabilities	13,979	13,267
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative liabilities	189	1,038
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member] | Foreign exchange derivative contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative liabilities	189	1,038
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	$ 6,152	$ 1,970