CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 41,246	$ 35,098
Other comprehensive income (loss) net of tax:
Net unrealized gain (loss) on available-for-sale investment securities	(17,079)	(10,360)
Reclassification adjustment of net gain (loss) from sale of available-for-sale securities included in net income	968	0
Related tax benefit (expense)	5,921	3,807
Other comprehensive income (loss) for available for sale securities, net of tax	(10,190)	(6,553)
Net unrealized gain (loss) on long-term borrowing hedge	29,271	2,795
Related tax benefit (expense)	(10,757)	(1,027)
Other comprehensive income (loss) on long term borrowing hedge, net of tax	18,514	1,768
Other comprehensive income (loss) net of tax	8,324	(4,785)
Comprehensive income	$ 49,570	$ 30,313