PARENT COMPANY ONLY FINANCIAL INFORMATION - Statements of Income (Details 1) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Statements, Captions [Line Items]
Interest income	$ 125,537	$ 109,253	$ 75,467
Interest expense	18,889	10,511	7,334
Net interest income	106,648	98,742	68,133
Income tax benefit	(13,446)	(16,267)	(9,371)
Net income	41,353	33,433	18,694
Nicolet Bankshares, Inc
Condensed Financial Statements, Captions [Line Items]
Interest income	52	46	58
Interest expense	2,844	2,415	1,951
Net interest income	(2,792)	(2,369)	(1,893)
Dividend income from subsidiaries	40,775	32,000	35,500
Operating expense	(364)	(369)	(202)
Gain (loss) on investments, net	265	1,411	(500)
Income tax benefit	305	1,329	833
Earnings before equity in undistributed income (loss) of subsidiaries	38,189	32,002	33,738
Equity in undistributed income (loss) of subsidiaries	2,847	1,148	(15,276)
Net income	$ 41,036	$ 33,150	$ 18,462