STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Comprehensive income:
Net income	$ 28,035	$ 28,206	$ 46,770	$ 40,790
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, 2014 and 2013, respectively	42	43	85	85
Other comprehensive income	42	43	85	85
Comprehensive income	$ 28,077	$ 28,249	$ 46,855	$ 40,875