NATURE OF BUSINESS AND SIGNIFICANT ACCOUNTING POLICIES - Narrative (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Nature Of Business And Significant Accounting Policies [Line Items]
Other investments	$ 17,997,000	$ 14,837,000
Restricted cash	6,300,000	$ 5,400,000	$ 0
Material loans criteria for ALLL adequacy calculation	$ 250,000
Core deposit intangibles
Nature Of Business And Significant Accounting Policies [Line Items]
Amortized period of core deposit intangible		10 years
Customer list intangibles:
Nature Of Business And Significant Accounting Policies [Line Items]
Amortized period of core deposit intangible		12 years
Nicolet Joint Ventures, LLC (the "JV")
Nature Of Business And Significant Accounting Policies [Line Items]
Ownership percentage	50.00%
United Financial Services Llc | As recorded by Baylake Corp
Nature Of Business And Significant Accounting Policies [Line Items]
Percentage of indirect interest			49.80%
Ownership percentage purchased by company			99.20%
Payment made for acquisition	$ 2,800,000	$ 2,600,000
United Financial Services Llc | Nicolet Joint Ventures, LLC (the "JV")
Nature Of Business And Significant Accounting Policies [Line Items]
Equity income recognized in business acquisition	1,800,000	1,300,000
Carrying value of bank investment	11,500,000	9,700,000
Accounting Standards Update 2016-01
Nature Of Business And Significant Accounting Policies [Line Items]
Other investments	2,700,000	$ 2,600,000
Cumulative effect of adoption of new accounting pronouncement	$ 77,000
Minimum | Securities sold under agreements to repurchase
Nature Of Business And Significant Accounting Policies [Line Items]
Maturity period of repo agreements	1 day
Maximum | Securities sold under agreements to repurchase
Nature Of Business And Significant Accounting Policies [Line Items]
Maturity period of repo agreements	4 days