Short and Long-Term Borrowings - Junior Subordinated Debentures (Details) - USD ($)	6 Months Ended
Jun. 30, 2020	Dec. 31, 2019
Junior Subordinated Debentures
Carrying Value	$ 417,826,000	$ 67,629,000
Junior subordinated debentures
Junior Subordinated Debentures
Par	38,249,000
Unamortized Discount	(7,434,000)
Carrying Value	30,815,000	30,575,000
Junior subordinated debentures \| 2005 Mid-Wisconsin Financial Services, Inc.
Junior Subordinated Debentures
Par	10,310,000
Unamortized Discount	(3,072,000)
Carrying Value	$ 7,238,000	$ 7,138,000
Effective percentage	1.74%	3.32%
Junior subordinated debentures \| 2006 Baylake Corp.
Junior Subordinated Debentures
Par	$ 16,598,000
Unamortized Discount	(3,765,000)
Carrying Value	$ 12,833,000	$ 12,715,000
Effective percentage	1.66%	3.31%
Junior subordinated debentures \| 2004 First Menasha Bancshares, Inc.
Junior Subordinated Debentures
Par	$ 5,155,000
Unamortized Discount	(597,000)
Carrying Value	$ 4,558,000	$ 4,536,000
Effective percentage	3.09%	4.69%
Junior subordinated debentures \| 2004 Nicolet Bankshares Statutory Trust
Junior Subordinated Debentures
Par	$ 6,186,000
Unamortized Discount	0
Carrying Value	$ 6,186,000	$ 6,186,000
Stated interest rate	8.00%
Junior subordinated debentures \| London Interbank Offered Rate (LIBOR) \| 2005 Mid-Wisconsin Financial Services, Inc.
Junior Subordinated Debentures
Floating interest rate	1.43%
Junior subordinated debentures \| London Interbank Offered Rate (LIBOR) \| 2006 Baylake Corp.
Junior Subordinated Debentures
Floating interest rate	1.35%
Junior subordinated debentures \| London Interbank Offered Rate (LIBOR) \| 2004 First Menasha Bancshares, Inc.
Junior Subordinated Debentures
Floating interest rate	2.79%

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

No definition available.

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- Definition

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

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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

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

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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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Amount, after accumulated amortization, of debt discount.

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- Definition

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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