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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Net income (numerator):
Net income	$ 6,665	$ 10,752	$ 12,008	$ 23,334
Shares (denominator):
Weighted average number of common shares outstanding used in basic computation (in shares)	19,963	20,463	20,098	20,436
Common shares issuable upon vesting of restricted stock (in shares)		47	1	39
Common shares issuable upon conversion of preferred shares (in shares)	10	10	10	10
Shares used in diluted computation (in shares)	19,973	20,520	20,109	20,485
Net income per common share
Basic (in dollars per share)	$ 0.33	$ 0.53	$ 0.60	$ 1.14
Diluted (in dollars per share)	$ 0.33	$ 0.52	$ 0.60	$ 1.14