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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Net income attributable to Nicolet Bankshares, Inc.	$ 13,530	$ 10,859	$ 42,346	$ 30,173
Weighted average common shares outstanding (in shares)	9,346,814	9,633,158	9,393,795	9,678,726
Effect of dilutive common stock awards (in shares)	350,000	316,000	313,000	325,000
Diluted weighted average common shares outstanding (in shares)	9,696,850	9,949,295	9,706,795	10,004,316
Basic earnings per common share (in dollars per share)	$ 1.45	$ 1.13	$ 4.51	$ 3.12
Diluted earnings per common share (in dollars per share)	$ 1.40	$ 1.09	$ 4.36	$ 3.02