Note 10 - Stock Repurchase Program - Schedule of Stock Purchases (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended																12 Months Ended		36 Months Ended
	Apr. 30, 2019		Apr. 30, 2021	[1]	Jan. 31, 2021	[1]	Oct. 31, 2020	[1]	Jul. 31, 2020	[1]	Apr. 30, 2020	[1]	Jan. 31, 2020	[1]	Oct. 31, 2019		Jul. 31, 2019	[1]	Apr. 30, 2021		Apr. 30, 2019	Dec. 31, 2016
Approximate Dollar Value of Shares That May Yet Be Purchased Under the Plan or Programs	$ 94		$ 2,823		$ 2,835		$ 2,835		$ 2,911		$ 3,019		$ 3,019		$ 3,206	[1]	$ 1,526		$ 2,823	[1]	$ 94	$ 750
Number of Shares Purchased (in shares)			17,303				152,915		212,000		25		267,468		206,050	[1]	120,821		3,103,633		2,127,051
Average Price Paid per Share (in dollars per share)			$ 0.65				$ 0.50		$ 0.51		$ 0.41		$ 0.70		$ 0.46	[1]	$ 0.35		$ 0.38		$ 0.31
Number of Shares Purchased as Part of Publicly Announced Plans or Programs (in shares)			17,303				152,915		212,000		25		267,468		206,050	[1]	120,821		3,103,633		2,127,051
Increase in program authorization, Approximate Dollar Value of Shares That May Yet Be Purchased Under the Plan or Programs	$ 1,569	[2]													$ 3,301	[3]

[1] These shares of common stock purchased were purchased through private transactions

[2] Board of Directors increased program authorization from $750 to $2,225

[3] Board of Directors increased program authorization from $2,225 to $4,000