Condensed Consolidated Statements Of Equity (USD $) In Thousands	Total		Common Stock [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]
Balances at Dec. 31, 2011	$ 1,261,919		$ 1,770	$ 737,015	$ (46,351)	$ 214,858	$ 354,627
Net income (loss)	(1,804,107)						(1,804,107)
Hedge derivative contract settlements reclassified into earnings from AOCI, net of income tax	(99,726)					(99,726)
Net change in derivative fair value, net of income tax	60,305	[1]				60,305
Foreign currency translation adjustment	(5,495)	[1]				(5,495)
Issuance and vesting of stock compensation	15,262		17	18,055	(2,810)
Stock option exercises	11		1	10
Balances at Sep. 30, 2012	(571,831)		1,788	755,080	(49,161)	169,942	(1,449,480)
Balances at Dec. 31, 2012	(1,132,797)		1,790	751,394	(49,495)	161,493	(1,997,979)
Net income (loss)	193,397						193,397
Hedge derivative contract settlements reclassified into earnings from AOCI, net of income tax	(37,181)					(37,181)
Net change in derivative fair value, net of income tax	0
Foreign currency translation adjustment	(933)					(933)
Issuance and vesting of stock compensation	12,996		47	14,421	(1,472)
Balances at Sep. 30, 2013	$ (964,518)		$ 1,837	$ 765,815	$ (50,967)	$ 123,379	$ (1,804,582)

[1] Note 1 contains additional information