Note 2 - Significant Accounting Policies - Earnings Per Share (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
BASIC
Net income	$ (628,349)	$ (121,534)	$ 1,440,092	$ 1,273,619	$ 1,671,340	$ 521,414	$ 1,027,732	$ 1,231,265	$ 1,963,828	$ 4,451,751	$ 6,402,259
Weighted average common shares outstanding (in shares)	9,143,746	9,154,209	9,180,076	9,264,446	9,270,862	9,270,862	9,225,960	9,308,726	9,185,203	9,242,092	9,301,867
Earnings per share – basic (in dollars per share)	$ (0.07)	$ (0.01)	$ 0.15	$ 0.14	$ 0.18	$ 0.06	$ 0.11	$ 0.13	$ 0.21	$ 0.48	$ 0.69
DILUTED
Net income	$ (628,349)	$ (121,534)	$ 1,440,092	$ 1,273,619	$ 1,671,340	$ 521,414	$ 1,027,732	$ 1,231,265	$ 1,963,828	$ 4,451,751	$ 6,402,259
Weighted average common shares outstanding (in shares)	9,143,746	9,154,209	9,180,076	9,264,446	9,270,862	9,270,862	9,225,960	9,308,726	9,185,203	9,242,092	9,301,867
Effect of restricted stock awards and assumed exercise of stock options (in shares)									459	14,718	19,691
Weighted average common shares outstanding, assuming dilution (in shares)	9,143,746	9,155,031	9,180,727	9,264,811	9,272,330	9,273,950	9,229,129	9,330,919	9,185,662	9,256,810	9,321,558
Earnings per share - diluted (in dollars per share)	$ (0.07)	$ (0.01)	$ 0.15	$ 0.14	$ 0.18	$ 0.06	$ 0.11	$ 0.13	$ 0.21	$ 0.48	$ 0.69
Outstanding options and restricted stock awards excluded as anti-dilutive (in shares)									657,717	17,632	31,477