STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Comprehensive income:
Net income	$ 18,735	$ 12,584
Derivative instruments:
Reclassification of losses to net income, net of tax of $24 for each of the three months ended March 31, 2014 and 2013	43	42
Other comprehensive income	43	42
Comprehensive income	$ 18,778	$ 12,626