Fair Value of Financial Assets and Liabilities Fair Value of Financial Assets and Liabilities, Changes in Level 3 Commodity Derivatives (Details) (Commodity Contract, USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Commodity Contract
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at beginning of period	$ 5,791,000		$ 9,933,000
Purchases	38,419,000		39,475,000
Settlements	(13,554,000)		(14,655,000)
Gains (losses) recognized as regulatory assets and liabilities	3,286,000		(811,000)
Balance at end of period	33,942,000	0	33,942,000	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	$ 0	$ 0	$ 0	$ 0