Fair Value of Financial Assets and Liabilities Fair Value of Financial Assets and Liabilities, Changes in Level 3 Commodity Derivatives (Details) (Commodity Contract [Member], USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 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
Purchases	1,056,000
Settlements	(1,101,000)
Losses recognized as regulatory assets and liabilities	(4,097,000)
Balance at end of period	5,791,000	0
Transfers into Level 3	0	0
Transfers out of Level 3	$ 0	$ 0