Derivative Commodity Instruments - Commodity Contracts by Business Segment (Details) (USD $)	Jun. 30, 2014 counterparty	Dec. 31, 2013	Jun. 30, 2013 bbl	Mar. 31, 2013 bbl
Derivative [Line Items]
Number of active counterparties with whom company holds net gain positions	2
Number of active counterparties with whom company holds net loss positions	12
Derivative assets	$ 1,147,000	$ 22,902,000
Notional Amount of Derivatives Transferred to Not Designated as Hedging Instruments			2,353,000	5,078,000
Net deferred tax liability	4,500,000	8,200,000
Cash Flow Hedging
Derivative [Line Items]
Derivative assets	$ 1,000,000