ACQUISITIONS - Summary of the Assets Acquired (Including Goodwill) and Liabilities Assumed, including Preliminary Purchase Price Allocation (Details) - USD ($) $ in Thousands		12 Months Ended		16 Months Ended
	Sep. 03, 2021	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2022	Dec. 31, 2021
Assets Acquired:
Goodwill		$ 367,387	$ 367,387	$ 367,387	$ 317,189
Assets Acquired:
Goodwill		0	228
Purchase Price:
Goodwill		0	$ 49,970
Mackinac Financial Corporation
Assets Acquired:
Cash and cash equivalents	$ 448,000	448,000
Investment securities	104,000	104,000
Loans	930,000	940,000
ACL-Loans	(6,000)	(2,000)
Premises and equipment	24,000	21,000
BOLI	16,000	16,000
Goodwill	20,000	0
Other intangibles	4,000	7,000
Other assets	25,000	22,000
Total assets	1,565,000	1,556,000
Liabilities Assumed:
Deposits	1,365,000	1,366,000
Borrowings	28,000	29,000
Other liabilities	13,000	14,000
Total liabilities	$ 1,406,000	1,409,000
Net assets acquired		$ 147,000
Assets Acquired:
Cash and cash equivalents				0
Investment securities				0
Loans				10,000
ACL-Loans				4,000
Premises and equipment				(3,000)
BOLI				0
Goodwill				(20,000)
Other intangibles				3,000
Other assets				(3,000)
Total assets				(9,000)
Liabilities Assumed:
Deposits				1,000
Borrowings				1,000
Other liabilities				1,000
Total liabilities				$ 3,000
Purchase Price:
Nicolet common stock issued (in shares)	2,337,230
Value of Nicolet common stock consideration	$ 180,000
Cash consideration paid	49,000
Total purchase price	229,000
Write-off prior investment in Mackinac	(2,000)
Goodwill	$ 84,000