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, 2019		Jun. 30, 2019		May 31, 2019		Jul. 31, 2019		Jul. 31, 2018	Apr. 30, 2019	[2],[3]
Balance, shares (in shares)	[1],[2],[3]					336,439		336,439
Balance, total average cost assigned	[1],[2],[3]					$ 4,743		$ 4,743
Balance, average cost per share (in dollars per share)	[1],[2],[3]					$ 14.10		$ 14.10
Balance, aggregate purchase price remaining under the program	[1]	$ 1,346	[2]	$ 1,346		$ 1,382		$ 1,346	[2]		$ 1,438
Purchases effected in open market, shares (in shares)	[1]			1,448		2,409
Purchases effected in open market, total average cost assigned			[1]	$ 36	[1]	$ 56	[1]	$ 92		$ 46
Purchases effected in open market, average cost per share (in dollars per share)	[1]			$ 24.98		$ 23.21
Balance, shares (in shares)	[1],[2]	340,296						340,296
Balance, total average cost assigned	[1],[2]	$ 4,835						$ 4,835
Balance, average cost per share (in dollars per share)	[1],[2]	$ 14.21						$ 14.21

[1] Includes 207,047 shares that were acquired during the $3 million repurchase program which was authorized in September 2012 and expired in October 2018.

[2] Includes 25,773 shares that were acquired during the $2 million repurchase program which was authorized in October 2018.

[3] Includes 85,219 shares 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.