Fair Value of Financial Assets and Liabilities, Changes in Level 3 Commodity Derivatives (Details) (Details) (Commodity Contract [Member], USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Commodity Contract [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at beginning of period	$ 9,933,000	$ 0
Purchases	50,244,000	9,933,000
Balance at end of period	15,884,000	9,933,000
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Settlements	(44,283,000)	0
Level 3 transfers, net	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Net Losses Gains Recognized As Regulatory Assets And Liabilities	$ (10,000)	$ 0