Earnings per Common Share - Calculations for basic and diluted earnings (loss) per common share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Earnings Per Share [Abstract]
Net income attributable to Nicolet Bankshares, Inc.	$ 10,555	$ 10,267
Weighted average common shares outstanding (in shares)	10,515,778	9,461,485
Effect of dilutive common stock awards (in shares)	285,000	297,000
Diluted weighted average common shares outstanding (in shares)	10,800,636	9,758,351
Basic earnings per common share (in dollars per share)	$ 1.00	$ 1.09
Diluted earnings per common share (in dollars per share)	$ 0.98	$ 1.05