Note 4 - Marketable Securities - Securities in a Continuous Loss Position (Details) - USD ($)	Mar. 31, 2018	Mar. 31, 2017
Fair market value, less than 12 months		$ 33,503,369
Gross unrealized losses, less than 12 months		(247,149)
Fair market value, greater than 12 months	$ 9,072,719
Gross unrealized losses, greater than 12 months
Total fair market value		33,503,369
Total gross unrealized losses		(247,149)
Corporate Bond Securities [Member]
Fair market value, less than 12 months	61,731,248	32,198,766
Gross unrealized losses, less than 12 months	(1,003,849)	(246,935)
Fair market value, greater than 12 months	9,072,719
Gross unrealized losses, greater than 12 months	(245,511)
Total fair market value	70,803,967	32,198,766
Total gross unrealized losses	$ (1,249,360)	(246,935)
Municipal Bonds [Member]
Fair market value, less than 12 months		1,304,603
Gross unrealized losses, less than 12 months		(214)
Fair market value, greater than 12 months
Gross unrealized losses, greater than 12 months
Total fair market value		1,304,603
Total gross unrealized losses		$ (214)