Derivative Financial Instruments (Narrative) (Details) $ in Thousands, bbl in Millions	3 Months Ended
	Mar. 31, 2016 USD ($) bbl	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($) bbl
Derivative [Line Items]
Energy commodity derivatives deposits, current liability	$ 6,903		$ 24,252
Energy commodity derivatives deposits, current asset	2,912		0
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months	(1,300)
Tank bottoms	$ 28,449		$ 27,533
Fair Value Hedging [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | bbl	0.7
Fair Value Hedging [Member] | NYMEX Commodity Contracts [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | bbl	0.7		0.7
Tank bottoms	$ (27,100)		$ (27,900)
Gain (Loss) from Components Excluded from Assessment of Fair Value Hedge Effectiveness, Net	(2,300)	$ 300
Two Thousand Fifteen Interest Rate Swaps [Member] | Cash Flow Hedging [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Derivative, Notional Amount	250,000
Derivative Liability, Fair Value, Gross Liability	$ 11,000