Note 13 - Treasury Stock and Repurchase Program - Treasury Stock at Cost (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
		Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2016		Apr. 30, 2015	[1]
Balance, shares (in shares)		288,335	243,411	190,504	[1]
Purchases effected in open market (2) (in shares)	[2]	20,045	44,924	52,907
Balance, shares (in shares)		308,380	288,335	243,411
Balance, total average cost assigned		$ 3,781	$ 3,040	$ 2,244	[1]
Purchases effected in open market (2)	[2]	354	741	796
Balance, total average cost assigned		$ 4,135	$ 3,781	$ 3,040
Balance, average cost per share (in dollars per share)		$ 13.11	$ 12.49	$ 11.78	[1]
Purchases effected in open market (2) (in dollars per share)	[2]	17.67	16.51	15.05
Balance, average cost per share (in dollars per share)		$ 13.41	$ 13.11	$ 12.49
Balance, aggregate purchase price remaining under the program		$ 255	$ 609	$ 1,350		$ 2,146

[1] Includes 85,219 shares with a total average cost of $1,036,000 that were acquired during the former repurchase program, which was authorized in January 2011 and expired in January 2012; 18,400 shares were acquired prior to January 2011.

[2] Were acquired during the $3 million repurchase program authorized in September 2012.