STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Comprehensive income:
Net income	$ 66,937	$ 35,037	$ 113,707	$ 75,827
Derivative instruments:
Reclassification of losses to net income, net of tax of $24 and $72 for each of the three and nine months ended Sept. 30, 2014 and 2013, respectively	44	44	129	129
Other comprehensive income	44	44	129	129
Comprehensive income	$ 66,981	$ 35,081	$ 113,836	$ 75,956