Acquisitions - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	Mar. 29, 2022	Dec. 03, 2021	Sep. 03, 2021	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021
Business Acquisition [Line Items]
Assets				$ 7,370,252		$ 7,695,037
Charter Bankshares, Inc.
Business Acquisition [Line Items]
Assets					$ 1,100,000
County Bancorp, Inc.
Business Acquisition [Line Items]
Cash paid per acquiree share (in dollars per share)		$ 37.18
Entity shares issued per acquiree share (in shares)		0.48
Shares exchanged for cash (in shares)		1,237,000
Number of common stock issued for consideration (in shares)		2,366,243
Value of Nicolet common stock consideration		$ 176,000
Cash consideration paid		48,000
Total purchase price		224,000
Assets		$ 1,405,000
Mackinac Financial Corporation
Business Acquisition [Line Items]
Cash paid per acquiree share (in dollars per share)			$ 4.64
Entity shares issued per acquiree share (in shares)			0.22
Number of common stock issued for consideration (in shares)			2,337,230
Value of Nicolet common stock consideration			$ 180,000
Cash consideration paid			49,000
Total purchase price			229,000
Assets			$ 1,565,000
Charter Bankshares, Inc.
Business Acquisition [Line Items]
Cash paid per acquiree share (in dollars per share)	$ 475
Entity shares issued per acquiree share (in shares)	15.458
Number of common stock issued for consideration (in shares)	1,260,000
Cash consideration paid	$ 38,800