Note 11 - Treasury Stock and Repurchase Program - Treasury Stock at Cost (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended				3 Months Ended
		Jul. 31, 2018	Jun. 30, 2018	May 31, 2018		Jul. 31, 2018	Jul. 31, 2017	Apr. 30, 2018	[1],[2]
Balance, shares (in shares)	[1],[2]			308,380		308,380
Balance, total average cost assigned	[1],[2]			$ 4,135		$ 4,135
Balance, average cost per share (in dollars per share)	[1],[2]			$ 13.41		$ 13.41
Balance, aggregate purchase price remaining under the program		$ 209		$ 209	[2]	$ 209		$ 255
Purchases effected in open market (in shares)				2,286	[2]
Purchases effected in open market, average cost assigned				$ 46	[2]	$ 46	$ 40
Purchases effected in open market, average cost per share (in dollars per share)				$ 20.26	[2]
Balance, shares (in shares)		310,666				310,666
Balance, total average cost assigned		$ 4,181				$ 4,181
Balance, average cost per share (in dollars per share)		$ 13.46				$ 13.46

[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.