Condensed Consolidated Statements Of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Statement of Income and Comprehensive Income [Abstract]
Net income	$ 46,586	$ 53,360	$ 79,723	$ 144,206
Other comprehensive income, net of taxes:
Change in value of derivative instruments used as cash flow hedges, net of tax of ($8,838), $27,015, $7,377 and $28,201	(14,137)	43,154	11,353	45,123
Reclassification - derivative settlements, Net of tax of ($5,523), ($771), ($14,793) and $1,008	(8,720)	(1,232)	(23,296)	1,608
Ineffective portion of derivatives, net of tax of $1,560, ($899), $1,792 and ($1,601)	2,455	(1,437)	2,829	(2,557)
Comprehensive income	$ 26,184	$ 93,845	$ 70,609	$ 188,380