Core Deposits and Other Intangibles - Intangible Assets Amortization Expense (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Sep. 30, 2019
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 11,049	$ 16,341
Accumulated amortization	(4,624)	(10,167)
Total	6,425	6,174
Core Deposit Intangible
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	7,339	7,339
Accumulated amortization	(4,133)	(3,518)
Total	3,206	3,821
Brand Intangible
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	0	8,464
Accumulated amortization	0	(6,392)
Total	0	2,072
Customer Relationships Intangible
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	3,172	0
Accumulated amortization	(183)	0
Total	2,989	0
Other Intangible
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	538	538
Accumulated amortization	(308)	(257)
Total	$ 230	$ 281