Condensed Consolidated Statements Of Comprehensive Income (Loss) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Statement of Income and Comprehensive Income [Abstract]
Net income (loss)	$ (19,302)	$ 49,819	$ 33,137	$ 90,846
Other comprehensive income, net of taxes:
Change in value of derivative instruments used as cash flow hedges, net of tax of $17,256, $10,371, $16,214 and $1,187	27,226	16,796	25,490	1,968
Reclassification - derivative settlements, Net of tax of ($6,106), $1,906, ($9,270) and $1,779	(9,564)	3,045	(14,576)	2,840
Ineffective portion of derivatives, net of tax of ($537), ($1,432), $232 and ($702)	(850)	(2,299)	374	(1,120)
Comprehensive income (loss)	$ (2,490)	$ 67,361	$ 44,425	$ 94,534