Note 9 - Share-based Compensation - Summary of Option Activity Under Stock Plans (Details) - USD ($)	6 Months Ended	12 Months Ended
	Sep. 30, 2017	Mar. 31, 2017
Outstanding (in shares)	503,000
Outstanding, weighted average exercise price (in dollars per share)	$ 4.10
Outstanding, weighted average remaining contractual term (Year)	4 years 328 days	4 years 255 days
Outstanding, aggregate intrinsic value	$ 261,755	$ 145,946
Granted (in shares)	75,000
Granted, weighted average exercise price (in dollars per share)	$ 3.35
Exercised (in shares)	(1,000)
Exercised, weighted average exercise price (in dollars per share)	$ 1.60
Forfeited (in shares)	(1,500)
Forfeited, weighted average exercise price (in dollars per share)	$ 3.11
Outstanding (in shares)	575,500	503,000
Outstanding, weighted average exercise price (in dollars per share)	$ 4.01	$ 4.10
Exercisable (in shares)	496,000
Exercisable, weighted average exercise price (in dollars per share)	$ 4.10
Exercisable, weighted average remaining contractual term (Year)	4 years 36 days
Exercisable, aggregate intrinsic value	$ 208,550