CONDENSED CONSOLIDATED STATEMENT OF COMPREHENSIVE INCOME (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 100,788		$ 69,889		$ 326,239		$ 201,827
Other comprehensive income (loss), net of taxes:
Reclassification adjustment for settled cash flow hedge contracts(1)	12,965	[1]	(11,942)	[1]	69,337	[1]	(22,372)	[1]
Changes in fair value of cash flow hedge contracts(2)	0	[2]	(1,447)	[2]	(80,175)	[2]	31,417	[2]
Postretirement benefits:
Amortization of net loss(3)	0	[3]	70	[3]	0	[3]	319	[3]
Total other comprehensive income (loss)	12,965		(13,319)		(10,838)		9,364
Comprehensive income (loss)	$ 113,753		$ 56,570		$ 315,401		$ 211,191

[1] Net of income taxes of $(8,592) and $7,742 for the three months ended September 30, 2014 and 2013, respectively, and $(45,951) and $14,504 for the nine months ended September 30, 2014 and 2013, respectively.

[2] Net of income taxes of $937 for the three months ended September 30, 2013 and $53,135 and $(20,366) for the nine months ended September 30, 2014 and 2013, respectively.

[3] Net of income taxes of $(46) and $(206) for the three and nine months ended September 30, 2013, respectively.