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Summary of Significant Accounting Policies (Details) $ in Millions			6 Months Ended
	Jul. 28, 2020 USD ($)	May 01, 2019 USD ($) shares	Jun. 30, 2020 segment	Jun. 30, 2019 USD ($)
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Number of operating segments \| segment			1
Subordinated debt
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Interest rate			6.50%
Subsequent event \| Subordinated debt \| 5.75% Fixed to floating subordinated notes
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Interest rate	5.75%
Subsequent event \| Subordinated debt \| 5.75% Fixed to floating subordinated notes \| Private placement
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Sale of equity	$ 65.0
MidWestOne Insurance Services Inc
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Gain on disposition of business				$ 1.1
ATBancorp
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Number of shares issued (in shares) \| shares		4,117,536
Value of equity interest issued		$ 116.0
Cash consideration		$ 34.8