Securities Available for Sale - Schedule of Available For Sale Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019
Amortized  Cost
Due in one year or less	$ 67,131	$ 58,377
Due after one year through five years	51,779	89,836
Due after five years through ten years	10,212	12,110
Due after ten years	0	0
Amortized  Cost	129,122	160,323
Estimated Fair Value
Due in one year or less	67,456	58,343
Due after one year through five years	52,694	90,601
Due after five years through ten years	10,642	12,324
Due after ten years	0	0
Estimated Fair Value	130,792	161,268
Amortized  Cost	1,726,962	1,765,284
Estimated Fair Value	1,774,626	1,783,208
Securities without contractual maturities, Amortized Cost	1,006	1,006
Securities without contractual maturities, Fair Value	1,054	1,037
Mortgage-backed securities
Estimated Fair Value
Amortized  Cost	1,596,834	1,603,955
Estimated Fair Value	$ 1,642,780	$ 1,620,903