Earnings per Common Share - Calculations for basic and diluted earnings (loss) per common share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings Per Share [Abstract]
Net income attributable to Nicolet Bankshares, Inc.	$ 7,824	$ 18,102	$ 44,347	$ 42,135
Weighted average common shares outstanding (in shares)	10,391,896	10,348,862	10,098,492	10,426,228
Effect of dilutive common stock awards (in shares)	384,000	150,000	405,000	179,000
Diluted weighted average common shares outstanding (in shares)	10,775,591	10,498,552	10,503,163	10,604,732
Basic earnings per common share (in dollars per share)	$ 0.75	$ 1.75	$ 4.39	$ 4.04
Diluted earnings per common share (in dollars per share)	$ 0.73	$ 1.72	$ 4.22	$ 3.97