CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 41,723	$ 40,361	$ 76,821	$ 78,768
Other comprehensive income (loss) net of tax:
Net unrealized gain (loss) on available-for-sale securities	6,916	5,063	(3,445)	13,623
Related tax benefit (expense)	(2,542)	(1,860)	1,266	(5,006)
Other comprehensive income (loss) for available for sale securities, net of tax	4,374	3,203	(2,179)	8,617
Net unrealized gain (loss) on long-term borrowing hedge	(13,483)	(4,985)	(10,688)	(9,233)
Related tax benefit (expense)	4,955	1,832	3,928	3,393
Other comprehensive income (loss) on long term borrowing hedge, net of tax	(8,528)	(3,153)	(6,760)	(5,840)
Other comprehensive income (loss) net of tax	(4,154)	50	(8,939)	2,777
Comprehensive income	$ 37,569	$ 40,411	$ 67,882	$ 81,545