Note 5 - Fair Value of Financial Instruments - Fair Value of Available-for-sale Securities (Details) - USD ($)
Sep. 30, 2018
Mar. 31, 2018
Total $ 76,576,286 $ 77,554,999
Less than 1 year 29,716,134  
1-3 years 22,784,235  
3-5 years $ 24,075,917