STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Comprehensive income:
Net income	$ 20,247	$ 18,735
Derivative instruments:
Reclassification of losses to net income, net of tax of $24 for each of the three months ended March 31, 2015 and 2014, respectively	42	43
Other comprehensive income	42	43
Comprehensive income	$ 20,289	$ 18,778