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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Net income attributable to Nicolet Bankshares, Inc.	$ 18,102	$ 13,530	$ 42,135	$ 42,346
Weighted average common shares outstanding (in shares)	10,348,862	9,346,814	10,426,228	9,393,795
Effect of dilutive common stock awards (in shares)	150,000	350,000	179,000	313,000
Diluted weighted average common shares outstanding (in shares)	10,498,552	9,696,850	10,604,732	9,706,795
Basic earnings per common share (in dollars per share)	$ 1.75	$ 1.45	$ 4.04	$ 4.51
Diluted earnings per common share (in dollars per share)	$ 1.72	$ 1.40	$ 3.97	$ 4.36