STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Comprehensive income:
Net income	$ 11,360	$ 10,238
Derivative instruments:
Reclassification of losses to net income, net of tax of $24, respectively	43	43
Other comprehensive income	43	43
Comprehensive income	$ 11,403	$ 10,281