Derivative Financial Instruments Derivative Financial Instruments (Narrative) (Details) bbl in Millions		3 Months Ended			12 Months Ended
		Mar. 31, 2015 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2015 USD ($) bbl	Dec. 31, 2014 USD ($) bbl	Dec. 31, 2013 USD ($)
Derivative [Line Items]
Energy commodity derivatives deposits					$ 24,252,000	$ 84,463,000
Debt Instrument, Face Amount					3,400,000,000.0	2,900,000,000.0
Net payment on financial derivatives					42,908,000	3,613,000	$ 184,000
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax	[1]				(14,904,000)	(30,090,000)	(4,744,000)
Energy commodity derivatives deposits					0	6,184,000
Tank bottoms					$ 27,533,000	$ 42,585,000
Cash Flow Hedging [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | bbl					0.0
Fair Value Hedging [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | bbl					0.7
Fair Value Hedging [Member] | Commodity Contract [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | bbl					0.7	0.7
Tank bottoms					$ (27,900,000)	$ (13,300,000)
Gain (Loss) on Fair Value Hedge Ineffectiveness, Net					1,000,000	(8,600,000)
Interest Expense [Member]
Derivative [Line Items]
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months					(1,400,000)
Two Thousand Fifteen Interest Rate Swaps [Member] | Cash Flow Hedging [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Derivative, Notional Amount					200,000,000.0
Derivative Asset, Fair Value, Gross Asset					2,200,000
Derivative Liability, Fair Value, Gross Liability					700,000
Two Thousand Fourteen Interest Rate Swaps [Member] | Cash Flow Hedging [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Derivative, Notional Amount		$ 250,000,000.0
Debt Instrument, Face Amount		$ 250,000,000.0
Debt Instrument, Interest Rate, Stated Percentage		4.20%
Net payment on financial derivatives		$ 42,900,000
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax	[1]				$ (16,400,000)	$ (26,500,000)
First Quarter 2014 Interest Rate Swaps [Member] | Cash Flow Hedging [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Derivative, Notional Amount			$ 200,000,000.0
Debt Instrument, Face Amount			$ 250,000,000.0
Debt Instrument, Interest Rate, Stated Percentage			5.15%
Net payment on financial derivatives			$ 3,600,000
Two Thousand Thirteen Interest Rate Swaps [Member] | Cash Flow Hedging [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Derivative, Notional Amount				$ 150,000,000.0			$ 150,000,000.0
Net payment on financial derivatives				$ 200,000

[1] See Note 13–Derivative Financial Instruments for details of the amount of gain/loss recognized in accumulated other comprehensive loss ("AOCL") on derivatives and the amount of gain/loss reclassified from AOCL into income.