Premises and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	$ 392,279	$ 389,036
Less accumulated depreciation and amortization	(155,268)	(145,974)
Premises and equipment, net	237,011	243,062
Land
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	90,726	92,938
Buildings
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	190,707	185,573
Leasehold improvements
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	18,081	18,361
Furniture, software and equipment
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	$ 92,765	$ 92,164
Minimum | Buildings
Property, Plant and Equipment [Line Items]
Estimated useful life	10 years
Minimum | Leasehold improvements
Property, Plant and Equipment [Line Items]
Estimated useful life	5 years
Minimum | Furniture, software and equipment
Property, Plant and Equipment [Line Items]
Estimated useful life	2 years
Maximum | Buildings
Property, Plant and Equipment [Line Items]
Estimated useful life	40 years
Maximum | Leasehold improvements
Property, Plant and Equipment [Line Items]
Estimated useful life	15 years
Maximum | Furniture, software and equipment
Property, Plant and Equipment [Line Items]
Estimated useful life	10 years