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, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net income available to common shareholders									$ 6,832,214	$ 9,415,090	$ 7,331,879
Weighted average common shares outstanding (in shares)									4,330,525	4,405,575	4,410,422
Effect of dilutive securities (in shares)									19,499	57,984	72,261
Weighted average diluted shares outstanding (in shares)									4,350,024	4,463,559	4,482,683
Basic income per common share (in dollars per share)	$ 0.22	$ 0.44	$ 0.43	$ 0.49	$ 0.54	$ 0.58	$ 0.55	$ 0.48	$ 1.58	$ 2.14	$ 1.66
Diluted income per common share (in dollars per share)	$ 0.22	$ 0.43	$ 0.43	$ 0.49	$ 0.53	$ 0.57	$ 0.54	$ 0.47	$ 1.57	$ 2.11	$ 1.64