PARENT COMPANY ONLY FINANCIAL INFORMATION - Statements of Cash Flows (Details 2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash Flows From Operating Activities:
Net income attributable to Nicolet Bankshares, Inc.	$ 41,353	$ 33,433	$ 18,694
Cash Flows From Financing Activities:
Purchase and retirement of common stock	(22,749)	(15,007)	(5,201)
Proceeds from issuance of common stock, net	1,800	4,030	1,900
Capitalized issuance costs, net	0	(186)	(260)
Redemption of preferred stock		0	(12,200)
Cash dividends paid on preferred stock		0	(633)
Net increase in cash and cash equivalents	94,593	25,830	45,484
Nicolet Bankshares, Inc
Cash Flows From Operating Activities:
Net income attributable to Nicolet Bankshares, Inc.	41,036	33,150	18,462
Adjustments to reconcile net income to net cash provided by operating activities:
Accretion of discounts	515	501	353
(Gain) loss on investments, net	(265)	(1,411)	500
Change in other assets and liabilities, net	(25)	(1,384)	395
Equity in undistributed (income) loss of subsidiaries, net of dividends	(2,847)	(1,148)	15,276
Net cash provided by operating activities	38,414	29,708	34,986
Cash Flows From Investing Activities:
Proceeds from sale of investments	708	317	565
Purchases of investments	(920)	0	0
Net cash paid in business combinations	0	(19,287)	(608)
Net cash provided by (used in) investing activities	(212)	(18,970)	(43)
Cash Flows From Financing Activities:
Purchase and retirement of common stock	(22,749)	(15,007)	(5,201)
Proceeds from issuance of common stock, net	1,800	4,030	1,900
Capitalized issuance costs, net	0	0	(260)
Repayment of long-term borrowings	0	0	(3,916)
Redemption of preferred stock	0	0	(12,200)
Cash dividends paid on preferred stock	0	0	(633)
Net cash provided by (used in) financing activities	(20,949)	(10,977)	(20,310)
Net increase in cash and cash equivalents	17,253	(239)	14,633
Beginning cash and due from subsidiary	28,026	28,265	13,632
Ending cash and due from subsidiary	$ 45,279	$ 28,026	$ 28,265