Note 2 - Significant Accounting Policies - Earnings Per Share (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	$ 1,671,340	$ 521,414	$ 1,027,732	$ 1,231,265	$ 2,059,997	$ 1,000,350	$ 1,820,915	$ 1,520,997	$ 4,451,751	$ 6,402,259	$ 6,402,405
Weighted average common shares outstanding (in shares)	9,270,862	9,270,862	9,225,960	9,308,726	9,188,483	9,188,483	9,209,446	9,698,951	9,242,092	9,301,867	10,077,506
Earnings per share – basic (in dollars per share)	$ 0.18	$ 0.06	$ 0.11	$ 0.13	$ 0.23	$ 0.11	$ 0.19	$ 0.16	$ 0.48	$ 0.69	$ 0.64
DILUTED
Net income	$ 1,671,340	$ 521,414	$ 1,027,732	$ 1,231,265	$ 2,059,997	$ 1,000,350	$ 1,820,915	$ 1,520,997	$ 4,451,751	$ 6,402,259	$ 6,402,405
Weighted average common shares outstanding (in shares)	9,270,862	9,270,862	9,225,960	9,308,726	9,188,483	9,188,483	9,209,446	9,698,951	9,242,092	9,301,867	10,077,506
Effect of restricted stock awards and assumed exercise of stock options (in shares)									14,718	19,691	25,254
Weighted average common shares outstanding, assuming dilution (in shares)	9,272,330	9,273,950	9,229,129	9,330,919	9,301,867	9,206,382	9,227,941	9,718,453	9,256,810	9,321,558	10,102,760
Earnings per share - diluted (in dollars per share)	$ 0.18	$ 0.06	$ 0.11	$ 0.13	$ 0.23	$ 0.11	$ 0.19	$ 0.16	$ 0.48	$ 0.69	$ 0.63
Outstanding options and restricted stock awards excluded as anti-dilutive (in shares)									17,632	31,477	60,433