Note 1 - Nature of Operations and Summary of Significant Accounting Policies - Earnings Per Common Share (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net income available to common shareholders									$ 9,415,090	$ 7,331,879	$ 5,157,664
Weighted average common shares outstanding (in shares)									4,405,575	4,410,422	4,372,262
Effect of dilutive securities (in shares)									57,984	72,261	68,685
Weighted average diluted shares outstanding (in shares)									4,463,559	4,482,683	4,440,947
Basic income per common share (in dollars per share)	$ 0.54	$ 0.58	$ 0.55	$ 0.48	$ 0.54	$ 0.89	$ (0.08)	$ 0.31	$ 2.14	$ 1.66	$ 1.18
Diluted income per common share (in dollars per share)	$ 0.53	$ 0.57	$ 0.54	$ 0.47	$ 0.53	$ 0.88	$ (0.08)	$ 0.30	$ 2.11	$ 1.64	$ 1.16