Note 3 - Net Income Per Share - Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Net income (numerator):
Net income	$ 6,349	$ 8,412	$ 10,777	$ 16,180
Shares (denominator):
Weighted average number of common shares outstanding used in basic computation (in shares)	20,178	20,063	20,144	20,024
Common shares issuable upon vesting of restricted stock (in shares)	380	81	230	64
Common shares issuable upon conversion of preferred shares (in shares)	10	10	10	10
Shares used in diluted computation (in shares)	20,568	20,154	20,384	20,098
Net income per common share
Basic (in dollars per share)	$ 0.31	$ 0.42	$ 0.53	$ 0.81
Diluted (in dollars per share)	$ 0.31	$ 0.42	$ 0.53	$ 0.81