Subordinated Debt - Schedule of Senior and Subordinated Debt (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Total junior subordinated debentures	$ 86,777	$ 86,311
Senior and subordinated debt	234,768	233,948
BST, BCT, GLST II, GLST III, and NSST I
Debt Instrument [Line Items]
Debt instrument, unamortized discount	6,700	7,200
Subordinated notes due in 2026
Debt Instrument [Line Items]
Subordinated notes	$ 147,991	$ 147,637
Interest rate	5.875%	5.875%
Junior Subordinated Debentures, First Midwest Capital Trust I \| First Midwest Capital Trust I (FMCT)
Debt Instrument [Line Items]
Total junior subordinated debentures	$ 37,806	$ 37,805
Interest rate	6.95%	6.95%
Junior Subordinated Debentures, Great Lakes Statutory Trust II \| Great Lakes Statutory Trust II (GLST II)
Debt Instrument [Line Items]
Total junior subordinated debentures	$ 4,769	$ 4,674
Basis spread on variable interest rate	1.40%	1.40%
Junior Subordinated Debentures, Great Lakes Statutory Trust III \| Great Lakes Statutory Trust III (GLST III)
Debt Instrument [Line Items]
Total junior subordinated debentures	$ 6,304	$ 6,187
Basis spread on variable interest rate	1.70%	1.70%
Junior Subordinated Debentures, Northern States Statutory Trust I \| Northern States Statutory Trust I (NSST I)
Debt Instrument [Line Items]
Total junior subordinated debentures	$ 8,339	$ 8,206
Basis spread on variable interest rate	1.80%	1.80%
Junior Subordinated Debentures, Bridgeview Statutory Trust I \| Bridgeview Statutory Trust I (BST)
Debt Instrument [Line Items]
Total junior subordinated debentures	$ 14,613	$ 14,542
Basis spread on variable interest rate	3.58%	3.58%
Junior Subordinated Debentures, Bridgeview Capital Trust II \| Bridgeview Capital Trust II (BCT)
Debt Instrument [Line Items]
Total junior subordinated debentures	$ 14,946	$ 14,897
Basis spread on variable interest rate	3.35%	3.35%

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

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Contractual interest rate for funds borrowed, under the debt agreement.

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Amount, after accumulated amortization, of debt discount.

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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.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Including the current and noncurrent portions, carrying value as of the balance sheet date of subordinated debt (with initial maturities beyond one year or beyond the operating cycle if longer). Subordinated debt places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets.

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