Derivative Instruments in the Balance Sheets (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Commodity Contracts
Assets
Gross Recognized Derivatives	$ 36,884	$ 49,951
Amounts Offset	(8,064)	(8,974)
Net Recognized Derivatives	28,820	40,977
Other	(481)	(7)
Amount Reported on Balance Sheet	29,301	40,984
Liabilities
Gross Recognized Derivatives	(92,429)	(122,663)
Amounts Offset	48,165	27,974
Net Recognized Derivatives	(44,264)	(94,689)
Other	(7,743)	(7,518)
Amount Reported on Balance Sheet	(52,007)	(102,207)
Assets and Liabilities
Gross Recognized Derivatives	(55,545)	(72,712)
Amounts Offset	40,101	19,000
Net Recognized Derivatives	(15,444)	(53,712)
Other	7,262	7,511
Amount Reported on Balance Sheet	(22,706)	(61,223)
Commodity Contracts | Current Assets
Assets
Gross Recognized Derivatives	16,172	24,587
Amounts Offset	(4,790)	(7,425)
Net Recognized Derivatives	11,382	17,162
Other	(481)	(7)
Amount Reported on Balance Sheet	11,863	17,169
Commodity Contracts | Investments and Other Assets
Assets
Gross Recognized Derivatives	20,712	25,364
Amounts Offset	(3,274)	(1,549)
Net Recognized Derivatives	17,438	23,815
Other	0	0
Amount Reported on Balance Sheet	17,438	23,815
Commodity Contracts | Current Liabilities
Liabilities
Gross Recognized Derivatives	(39,236)	(50,540)
Amounts Offset	19,357	26,166
Net Recognized Derivatives	(19,879)	(24,374)
Other	(7,743)	(7,518)
Amount Reported on Balance Sheet	(27,622)	(31,892)
Commodity Contracts | Deferred Credits and Other
Liabilities
Gross Recognized Derivatives	(53,193)	(72,123)
Amounts Offset	28,808	1,808
Net Recognized Derivatives	(24,385)	(70,315)
Other	0	0
Amount Reported on Balance Sheet	(24,385)	(70,315)
Designated as Hedging Instruments
Liabilities
Gross Recognized Derivatives	$ (4,000)	$ (5,000)