Condensed Consolidated Statements Of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Condensed Consolidated Statements Of Comprehensive Income [Abstract]
Net income	$ 52,439	$ 41,027
Other comprehensive income, net of taxes:
Change in value of derivative instruments used as cash flow hedges, net of tax of ($1,041) and ($9,184)	(1,736)	(14,827)
Reclassification - derivative settlements, Net of tax of ($3,164) and ($127)	(5,012)	(205)
Ineffective portion of derivatives, net of tax of $769 and $730	1,224	1,179
Comprehensive income	$ 46,915	$ 27,174