CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 265,272	$ 432,573	$ 340,822
Other comprehensive income/(losses):
Unrealized holding gain/(losses)	(4,690)	(4,061)	4,208
Gains/(losses) reclassified to net income	3,624	(228)	834
Total other comprehensive income (loss)	(1,066)	(4,289)	5,042
Comprehensive income	$ 264,206	$ 428,284	$ 345,864