Derivative Financial Instruments (Narrative) (Details) $ in Thousands, bbl in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016 USD ($) bbl	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) bbl	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($) bbl
Derivative [Line Items]
Energy commodity derivatives deposits, current asset	$ 28,528		$ 28,528		$ 0
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months			(1,200)
Tank bottoms	35,492		35,492		$ 27,533
Cash Flow Hedging [Member] | Interest Rate Contract [Member] | Other Current Liabilities [Member]
Derivative [Line Items]
Derivative, Notional Amount	250,000		250,000
Derivative Liability, Fair Value, Gross Liability	18,600		18,600
Cash Flow Hedging [Member] | Interest Rate Contract [Member] | Other Noncurrent Liabilities [Member]
Derivative [Line Items]
Derivative, Notional Amount	100,000		100,000
Derivative Liability, Fair Value, Gross Liability	1,400		1,400
Cash Flow Hedging [Member] | Interest Rate Contract [Member] | Other Noncurrent Assets [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 400		$ 400
Fair Value Hedging [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | bbl	0.7		0.7
Fair Value Hedging [Member] | NYMEX Commodity Contracts [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | bbl	0.7		0.7		0.7
Tank bottoms	$ (17,500)		$ (17,500)		$ (27,900)
Gain (Loss) from Components Excluded from Assessment of Fair Value Hedge Effectiveness, Net	$ 1,900	$ 6,500	$ 4,200	$ 6,300