Derivatives Commodity Instruments - Cash Flow Hedging Relationship in Financial Statements (Details) - Commodity contracts - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Net gain recognized in other comprehensive income on derivatives (effective portion), net of tax of $18 and $25		$ 29		$ 40
Unrealized gain (loss) on derivatives arising during period, tax	$ 0	18	$ 0	25
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)		$ 5,992		$ 15,781