Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Comprehensive income
Net income	$ 38,900	$ 40,463	$ 37,710	$ 50,245
Other comprehensive loss
Reclassification adjustment for hedge gains included in gain from oil hedging activities in the consolidated statements of operations	(9,509)	(11,886)	(19,512)	(24,309)
Income tax benefit related to other comprehensive loss	3,642	5,844	7,460	10,588
Other comprehensive loss, net of tax	(5,867)	(6,042)	(12,052)	(13,721)
Comprehensive income	$ 33,033	$ 34,421	$ 25,658	$ 36,524