Note 9 - Stock Options Under the Plans (Details) - $ / shares	3 Months Ended
	Jul. 31, 2016	Jul. 31, 2015
Beginning Balance, shares underlying options (in shares)	89,303
Beginning Balance, weighted average exercise price (in dollars per share)	$ 42.90
Balance, weighted average remaining contractual term	6 years 109 days	3 years 219 days
Forfeited (in shares)	(735)
Forfeited. (in dollars per share)	$ 56.39
Exercised (in shares)
Exercised. (in dollars per share)
Granted (in shares)	72,874
Granted. (in dollars per share)	$ 1.58
Ending Balance, shares underlying options (in shares)	161,442
Ending Balance, weighted average exercise price+ (in dollars per share)	$ 24.19
Exerciser, shares underlying options (in shares)	81,482
Exercisable, weighted average exercise price (in dollars per share)	$ 45.49
Exercisable, weighted average remaining contractual term	3 years 36 days