Long-Term Debt - Junior Subordinated Notes (Details) - Junior subordinated notes - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Mar. 31, 2021	Jun. 30, 2020	Dec. 31, 2020
Debt Instrument [Line Items]
Debt instrument, face amount	$ 44,847		$ 44,847
Debt instrument, book value	$ 41,807		41,763
Stated maturity date	5 years
ATBancorp Statutory Trust I
Debt Instrument [Line Items]
Debt instrument, face amount	$ 7,732		7,732
Debt instrument, book value	$ 6,859		$ 6,850
Interest rate	1.86%		1.90%
ATBancorp Statutory Trust I \| LIBOR
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	1.68%	1.68%
ATBancorp Statutory Trust II
Debt Instrument [Line Items]
Debt instrument, face amount	$ 12,372		$ 12,372
Debt instrument, book value	$ 10,864		$ 10,850
Interest rate	1.83%		1.87%
ATBancorp Statutory Trust II \| LIBOR
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	1.65%	1.65%
Barron Investment Capital Trust I
Debt Instrument [Line Items]
Debt instrument, face amount	$ 2,062		$ 2,062
Debt instrument, book value	$ 1,775		$ 1,767
Interest rate	2.35%		2.39%
Barron Investment Capital Trust I \| LIBOR
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	2.15%	2.15%
Central Bancshares Capital Trust II
Debt Instrument [Line Items]
Debt instrument, face amount	$ 7,217		$ 7,217
Debt instrument, book value	$ 6,845		$ 6,832
Interest rate	3.68%		3.72%
Central Bancshares Capital Trust II \| LIBOR
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	3.50%	3.50%
MidWestOne Statutory Trust II
Debt Instrument [Line Items]
Debt instrument, face amount	$ 15,464		$ 15,464
Debt instrument, book value	$ 15,464		$ 15,464
Interest rate	1.77%		1.81%
MidWestOne Statutory Trust II \| LIBOR
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	1.59%	1.59%

Debt Instrument, Payment Deferment Period

No definition available.

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- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

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- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28551-108399

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-Section 55
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-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

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- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120520924&loc=SL6036836-161870

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-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Including the current and noncurrent portions, the carrying value of junior subordinated long-term debt owed to unconsolidated subsidiary trusts as of the balance sheet date. Such debt places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets and was initially scheduled to be repaid after one year or beyond the normal operating cycle if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

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-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

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