Loans and Allowance for Credit Losses - Classes of loans information (Details) - USD ($)			3 Months Ended
	Jan. 20, 2023	Feb. 25, 2022	Sep. 30, 2024	Sep. 30, 2023	Jun. 30, 2024
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans (before deferred loan fees, net)			$ 3,966,736,000		$ 3,850,035,000
Provision for credit losses			2,159,000	$ 900,000
Allowance for credit losses, loans			2,021,000	1,570,000
Provision (recovery) for off balance sheet credit exposure			$ 138,000	$ (670,000)
Net charge offs on average loans outstanding (as percentage)			0.01%	0.03%
Citizens Bancshares Company
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses for purchased credit deteriorated (PCD)	$ 1,121,000
Fortune
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses for purchased credit deteriorated (PCD)		$ 120,000
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortization period of loans			5 years
Total loans (before deferred loan fees, net)			$ 457,018,000		450,147,000
Allowance for credit losses, loans			(85,000)	$ (100,000)
Provision (recovery) for off balance sheet credit exposure			20,000	37,000
Agriculture production
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans (before deferred loan fees, net)			200,215,000		175,968,000
Allowance for credit losses, loans			(51,000)	(85,000)
Provision (recovery) for off balance sheet credit exposure			(3,000)	(84,000)
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans (before deferred loan fees, net)			58,735,000		59,671,000
Allowance for credit losses, loans			$ 13,000	38,000
Provision (recovery) for off balance sheet credit exposure				1,000
Consumer | Automobile loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maximum percentage of appraised value or purchase price that loans cannot exceed			100.00%
Amortization period of loans			66 months
Consumer | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortization period of loans			66 months
Consumer | Maximum | Home Equity Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortization period of loans			10 years
All other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans (before deferred loan fees, net)			$ 3,699,000		3,981,000
Allowance for credit losses, loans			(3,000)	(5,000)
Provision (recovery) for off balance sheet credit exposure				(3,000)
Secured by real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans (before deferred loan fees, net)			$ 3,247,069,000		3,160,268,000
Secured by real estate | 1-4 residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maximum percentage of appraised value or purchase price that loans cannot exceed			90.00%
Total loans (before deferred loan fees, net)			$ 942,916,000		925,397,000
Allowance for credit losses, loans			157,000	(101,000)
Provision (recovery) for off balance sheet credit exposure			$ 30,000	5,000
Secured by real estate | 1-4 residential real estate | Home Equity Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of appraised value or estimated value of property			90.00%
Term of loan			10 years
Secured by real estate | 1-4 residential real estate | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fixed-rate and adjustable-rate mortgage (ARM) loans amortization period (in years)			30 years
Secured by real estate | Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans (before deferred loan fees, net)			$ 1,600,000,000
Secured by real estate | Commercial Real Estate | Secured by properties located outside lending area
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans (before deferred loan fees, net)			$ 626,300,000
Secured by real estate | Commercial Real Estate | Non-owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maximum percentage of appraised value or purchase price that loans cannot exceed			80.00%
Total loans (before deferred loan fees, net)			$ 903,678,000		899,770,000
Term of variable interest applicability on loans			7 years
Allowance for credit losses, loans			$ 1,673,000	2,641,000
Provision (recovery) for off balance sheet credit exposure			$ 22,000
Secured by real estate | Commercial Real Estate | Non-owner occupied | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortization period of loans			25 years
Term of fixed interest applicability on loans			10 years
Secured by real estate | Commercial Real Estate | Owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans (before deferred loan fees, net)			$ 438,030,000		427,476,000
Allowance for credit losses, loans			(1,000)	(289,000)
Provision (recovery) for off balance sheet credit exposure			$ (14,000)	(2,000)
Secured by real estate | Multi-family real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maximum percentage of appraised value or purchase price that loans cannot exceed			85.00%
Total loans (before deferred loan fees, net)			$ 371,177,000		384,564,000
Allowance for credit losses, loans			(376,000)	(612,000)
Provision (recovery) for off balance sheet credit exposure			$ 3,000	(1,000)
Secured by real estate | Multi-family real estate | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortization period of loans			25 years
Amortization term of ballon maturity			10 years
Secured by real estate | Construction and land development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortization period of loans			25 years
Total loans (before deferred loan fees, net)			$ 351,481,000		290,541,000
Allowance for credit losses, loans			774,000	224,000
Provision (recovery) for off balance sheet credit exposure			$ 88,000	(612,000)
Secured by real estate | Construction and land development | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maturities of single-family residential construction loans			6 months
Maturities of multifamily or commercial construction loans			12 months
Secured by real estate | Construction and land development | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortization period of loans			30 years
Maturities of single-family residential construction loans			12 months
Maturities of multifamily or commercial construction loans			36 months
Secured by real estate | Agriculture real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortization period of loans			1 year
Total loans (before deferred loan fees, net)			$ 239,787,000		$ 232,520,000
Agricultural real estate terms if 75% loan-to-value ratio			30 years
Allowance for credit losses, loans			$ (80,000)	(141,000)
Provision (recovery) for off balance sheet credit exposure			$ (8,000)	$ (11,000)
Secured by real estate | Agriculture real estate | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Agricultural real estate terms if 80% loan-to-value ratio			25 years