STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Comprehensive income:
Net income	$ 30,294	$ 24,672	$ 41,654	$ 34,910
Derivative instruments:
Reclassification of losses to net income, net of tax of $24 and $48 for each of the three and six months ended June 30, 2012 and 2011, respectively	43	43	86	86
Other comprehensive income	43	43	86	86
Comprehensive income	$ 30,337	$ 24,715	$ 41,740	$ 34,996