ACQUISITIONS - Narrative (Details) $ / shares in Units, $ in Thousands					12 Months Ended
	Aug. 26, 2022 USD ($) $ / shares shares	Dec. 03, 2021 USD ($) $ / shares shares	Sep. 03, 2021 USD ($) $ / shares shares	Aug. 21, 2020 USD ($) branch	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Aug. 20, 2020
Business Acquisition [Line Items]
Acquisitions					$ 49,970	$ 154,038
Advantage Community Bancshares, Inc.
Business Acquisition [Line Items]
Percentage of assets represented by acquiree							0.04
Charter Bankshares, Inc.
Business Acquisition [Line Items]
Entity shares issued per acquiree share (in shares) | shares	15.458
Cash paid per acquiree share (in dollars per share) | $ / shares	$ 475
Nicolet common stock issued (in shares) | shares	1,262,360
Value of Nicolet common stock consideration	$ 98,000
Cash consideration paid	39,000
Total purchase price	137,000
Total assets	1,110,000				1,121,000
Acquisitions	$ 50,000
County Bancorp, Inc.
Business Acquisition [Line Items]
Entity shares issued per acquiree share (in shares) | shares		0.48
Cash paid per acquiree share (in dollars per share) | $ / shares		$ 37.18
Nicolet common stock issued (in shares) | shares		2,366,243
Value of Nicolet common stock consideration		$ 176,000
Cash consideration paid		48,000
Total purchase price		$ 224,000
Shares exchanged for cash (in shares) | shares		1,237,000
Total assets		$ 1,405,000			$ 1,412,000
Acquisitions		$ 70,000
Mackinac Financial Corporation
Business Acquisition [Line Items]
Entity shares issued per acquiree share (in shares) | shares			0.22
Cash paid per acquiree share (in dollars per share) | $ / shares			$ 4.64
Nicolet common stock issued (in shares) | shares			2,337,230
Value of Nicolet common stock consideration			$ 180,000
Cash consideration paid			49,000
Total purchase price			$ 229,000
Cash paid per acquiree share (in percent)			20.00%
Entity shares issued per acquiree share (in percent)			80.00%
Acquisitions			$ 84,000
Advantage Community Bancshares, Inc.
Business Acquisition [Line Items]
Number of branches | branch				4
Total assets				$ 172,000
Loans acquired				88,000
Deposits acquired				141,000
Acquisitions				12,000
Advantage Community Bancshares, Inc. | Core deposit intangibles:
Business Acquisition [Line Items]
Intangible assets acquired				$ 1,000