Condensed Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 81,382	$ 97,114	$ 216,386	$ 242,820
Unrealized gain (loss) on interest rate derivative instruments, net of deferred taxes of $0, ($320), $0 and ($511)	0	(553)	0	(909)
Unrealized gain (loss) on investment securities, net of deferred taxes of $3, $0, $3 and $0	4	0	4	0
Interest rate swap losses reclassified into earnings, net of taxes of $32, $15, $97 and $15	56	25	170	25
Other comprehensive income (loss)	60	(528)	174	(884)
Comprehensive income	$ 81,442	$ 96,586	$ 216,560	$ 241,936