Derivative Commodity Instruments (Cash Flow Hedging Relationship in Financial Statements) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Net gain (loss) recognized in other comprehensive income on derivatives (effective portion), net of tax of $23 and ($6,660)	$ 37	$ (10,866)
Gain (loss) recognized in other comprehensive income on derivatives	23	(6,660)
Gain (Loss) on Derivative Instruments, Net
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain reclassified from accumulated other comprehensive income into income (effective portion)	21,612	34,293
Gain (loss) recognized in income on derivatives (ineffective portion and amount excluded from effectiveness testing)	$ 0	$ 835