Core Deposits and Other Intangibles - Intangible Assets Amortization Expense (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 11,049	$ 16,341
Accumulated amortization	(4,885)	(10,167)
Net intangible assets	6,164	6,174
Core Deposit Intangible
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	7,339	7,339
Accumulated amortization	(4,316)	(3,518)
Net intangible assets	3,023	3,821
Brand Intangible
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	0	8,464
Accumulated amortization	0	(6,392)
Net intangible assets	0	2,072
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	3,172	0
Accumulated amortization	(244)	0
Net intangible assets	2,928	0
Other Intangible
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	538	538
Accumulated amortization	(325)	(257)
Net intangible assets	$ 213	$ 281