Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 29,230	$ 36,903
Securities available for sale:
Net unrealized holding (loss) arising during the year	(8,645)	(21,468)
Reclassification adjustment for net loss realized in net income	1	0
Income tax benefit	3,283	8,158
Net change in unrealized (losses) on securities available for sale	(5,361)	(13,310)
Defined benefit pension plan obligation:
Net unrealized holding gain arising during the year	145	0
Income tax (expense)	(55)	0
Net change in defined benefit pension plan obligation	90	0
Other comprehensive (loss), net of tax	(5,271)	(13,310)
Comprehensive income	$ 23,959	$ 23,593