Securities Available for Sale - Schedule of Available For Sale Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017
Amortized Cost
Due in one year or less	$ 111,842	$ 91,535
Due after one year through five years	114,920	193,117
Due after five years through ten years	11,076	16,306
Due after ten years	122	122
Amortized Cost	237,960	301,080
Estimated Fair Value
Due in one year or less	111,221	91,597
Due after one year through five years	113,069	193,373
Due after five years through ten years	10,535	16,097
Due after ten years	122	122
Estimated Fair Value	234,947	301,189
Amortized Cost	1,427,454	1,376,942
Estimated Fair Value	1,385,650	1,367,960
Securities without contractual maturities, Amortized Cost	1,006	1,006
Securities without contractual maturities, Fair Value	996	1,034
Mortgage-backed securities
Estimated Fair Value
Amortized Cost	1,188,488	1,074,856
Estimated Fair Value	$ 1,149,707	$ 1,065,737