CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Comprehensive income:
Net income	$ 173,081	$ 154,159	$ 382,547	$ 362,354
Derivative instruments:
Net fair value decrease, net of tax of $(12), $(10), $(10), and $(9), respectively	(17)	(17)	(14)	(15)
Reclassification of losses (gains) to net income, net of tax of $5, $(72), $(123) and $(217), respectively	19	(119)	(192)	(356)
Other comprehensive income (loss)	2	(136)	(206)	(371)
Comprehensive income	$ 173,083	$ 154,023	$ 382,341	$ 361,983