Condensed Consolidated Statements Of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Statement of Other Comprehensive Income [Abstract]
Net income	$ 40,206	$ 52,439
Other comprehensive income, net of taxes:
Change in value of derivative instruments used as cash flow hedges, net of tax of ($6,378) and ($1,041)	(9,911)	(1,736)
Reclassification - derivative settlements, net of tax of ($1,494) and ($3,164)	(2,337)	(5,012)
Ineffective portion of derivatives, net of tax of $526 and $768	823	1,224
Comprehensive income	$ 28,781	$ 46,915