STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Comprehensive income:
Net income	$ 61,815	$ 66,937	$ 104,638	$ 113,707
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, 2015 and 2014, respectively	44	44	129	129
Other comprehensive income	44	44	129	129
Comprehensive income	$ 61,859	$ 66,981	$ 104,767	$ 113,836