Consolidated Statements of Comprehensive Income (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Statement of Other Comprehensive Income [Abstract]
Net income	$ 23,064	$ 32,602
Other comprehensive income, net of tax:
Net change in fair value of derivatives, net of tax expense of $289 and $118 for the three months ended, March 31, 2012 and 2013, respectively	3,826	16,483
Cash flow hedges reclassified into earnings	8,274	4,071
Other comprehensive income	12,100	20,554
Total comprehensive income	$ 35,164	$ 53,156