STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Comprehensive income:
Net income	$ 95,177	$ 106,369	$ 89,901
Derivative instruments:
Reclassification of losses to net income, net of tax of $97, $97 and $98, respectively	171	172	171
Other comprehensive income	171	172	171
Comprehensive income	$ 95,348	$ 106,541	$ 90,072