Note 11 - Treasury Stock and Repurchase Program - Treasury Stock at Cost (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		6 Months Ended
		Oct. 31, 2017	Jul. 31, 2017	Oct. 31, 2017	Oct. 31, 2016	Apr. 30, 2017	[1],[2]
Balance, shares (in shares)	[1],[2]		288,335	288,335
Balance, total average cost assigned	[1],[2]		$ 3,781	$ 3,781
Balance, average cost per share (in dollars per share)	[1],[2]		$ 13.11	$ 13.11
Balance, aggregate purchase price remaining under the program		$ 459	$ 569	$ 459		$ 609
Purchases effected in open market, shares (in shares)		6,512	2,353
Purchases effected in open market, total average cost assigned		$ 110	$ 40	$ 150	$ 681
Purchases effected in open market, average cost per share (in dollars per share)		$ 16.90	$ 17.29
Balance, shares (in shares)		297,200		297,200
Balance, total average cost assigned		$ 3,931		$ 3,931
Balance, average cost per share (in dollars per share)		$ 13.23		$ 13.23

[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.