Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Statement of Comprehensive Income [Abstract]
Net (loss) income	$ (740,618)	$ 44,511	$ (697,344)	$ 90,297
Securities available for sale:
Net unrealized holding gain arising during the period	38,341	11,523	30,181	30,192
Reclassification adjustment for net loss realized in net income	0	0	0	513
Income tax expense	(9,450)	(2,839)	(7,440)	(7,568)
Net change in unrealized gain on securities available for sale	28,891	8,684	22,741	23,137
Comprehensive (loss) income	$ (711,727)	$ 53,195	$ (674,603)	$ 113,434