Note 5 - Marketable Securities - Securities in a Continuous Loss Position (Details) - USD ($)	9 Months Ended	12 Months Ended
	Dec. 31, 2017	Mar. 31, 2017
Fair market value, less than 12 months	$ 44,282,521	$ 33,503,369
Gross unrealized losses, less than 12 months	(325,912)	(247,149)
Fair market value, greater than 12 months	9,224,878
Gross unrealized losses, greater than 12 months	(119,294)
Total fair market value	53,507,399	33,503,369
Total gross unrealized losses	(445,206)	(247,149)
Corporate Bond Securities [Member]
Fair market value, less than 12 months	44,282,521	32,198,766
Gross unrealized losses, less than 12 months	(325,912)	(246,935)
Fair market value, greater than 12 months	9,224,878
Gross unrealized losses, greater than 12 months	(119,294)
Total fair market value	53,507,399	32,198,766
Total gross unrealized losses	(445,206)	(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)