Earnings per Common Share - Calculations for basic and diluted earnings (loss) per common share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share [Abstract]
Net income attributable to Nicolet Bankshares, Inc.	$ 13,478	$ 18,549	$ 24,033	$ 28,816
Weighted average common shares outstanding (in shares)	10,417,226	9,374,348	10,466,590	9,417,676
Effect of dilutive common stock awards (in shares)	103,000	318,000	192,000	293,000
Diluted weighted average common shares outstanding (in shares)	10,519,739	9,692,378	10,659,318	9,710,827
Basic earnings per common share (in dollars per share)	$ 1.29	$ 1.98	$ 2.30	$ 3.06
Diluted earnings per common share (in dollars per share)	$ 1.28	$ 1.91	$ 2.25	$ 2.97