Condensed Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 61,920	$ 69,002
Unrealized loss on interest rate derivative instruments, net of deferred tax benefit of $0 and $940	0	(1,594)
Losses reclassified from other comprehensive income	90	0
Other comprehensive income (loss)	90	(1,594)
Comprehensive income	$ 62,010	$ 67,408