STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Comprehensive income:
Net income	$ 22,576	$ 28,035	$ 42,823	$ 46,770
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, 2015 and 2014, respectively	43	42	85	85
Other comprehensive income	43	42	85	85
Comprehensive income	$ 22,619	$ 28,077	$ 42,908	$ 46,855