Note 5 - Marketable Securities - Gross Unrealized Losses and Fair Value of Investments (Details) - USD ($)	3 Months Ended	12 Months Ended
	Jun. 30, 2017	Mar. 31, 2017
Gross unrealized losses, less than 12 months	$ (154,828)	$ (247,149)
Fair market value, greater than 12 months
Gross unrealized losses, greater than 12 months
Total fair market value	43,200,362	33,503,369
Total gross unrealized losses	(154,828)	(247,149)
Fair market value, less than 12 months	43,200,362	33,503,369
Corporate Bond Securities [Member]
Gross unrealized losses, less than 12 months	(154,146)	(246,935)
Fair market value, greater than 12 months
Gross unrealized losses, greater than 12 months
Total fair market value	41,906,105	32,198,766
Total gross unrealized losses	(154,146)	(246,935)
Fair market value, less than 12 months	41,906,105	32,198,766
Municipal Bonds [Member]
Gross unrealized losses, less than 12 months	(682)	(214)
Fair market value, greater than 12 months
Gross unrealized losses, greater than 12 months
Total fair market value	1,294,257	1,304,603
Total gross unrealized losses	(682)	(214)
Fair market value, less than 12 months	$ 1,294,257	$ 1,304,603