Note 17 - Earnings Per Share - Basic and Diluted (Details) - USD ($)		3 Months Ended								12 Months Ended
		Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net income		$ 9,901,590	$ 7,853,935	$ 8,766,017	$ 9,184,965	$ 8,529,330	$ 6,107,501	$ 6,676,467	$ 6,373,489	$ 35,706,507	$ 27,686,787	$ 16,927,881
Basic earnings per common share (in dollars per share)		$ 0.72	$ 0.60	$ 0.67	$ 0.70	$ 0.65	$ 0.47	$ 0.54	$ 0.54	$ 2.68	$ 2.20	$ 1.64
Diluted earnings per common share (in dollars per share)		$ 0.70	$ 0.58	$ 0.65	$ 0.68	$ 0.64	$ 0.46	$ 0.53	$ 0.53	$ 2.61	$ 2.17	$ 1.61
Weighted average common shares outstanding (in shares)	[1]									13,325,128	12,570,767	10,345,286
Weighted average common shares issuable upon exercise of stock options and under the employee stock purchase plan** (in shares)	[2]									355,344	195,236	154,555
Weighted average common and common equivalent shares outstanding (in shares)										13,680,472	12,766,003	10,499,841

[1] The increase in weighted average common shares outstanding from 2015 to 2016 was primarily due to the common stock issuance that occurred in conjunction with the CSB acquisition.

[2] Excludes anti-dilutive shares of 49,919, 17,739, and 36,572 at December 31,2017, 2016 and 2015, respectively.