Note 5 - Revenue Recognition (Details Textual) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Jun. 30, 2018
Contract with Customer, Liability, Total	$ 367,198	$ 424,574
Contract with Customer, Liability, Total		$ 763,252	$ 859,370
Minimum [Member]
Contract with Customer, Liability, Remaining Performance Obligation, Expected Timing of Satisfaction, Period (Year)	1 year
Maximum [Member]
Contract with Customer, Liability, Remaining Performance Obligation, Expected Timing of Satisfaction, Period (Year)	3 years