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		9 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Net income (numerator):
Net income	$ 6,840	$ 7,787	$ 18,848	$ 31,121
Shares (denominator):
Weighted average number of common shares outstanding used in basic computation (in shares)	19,984	20,483	20,060	20,452
Common shares issuable upon vesting of restricted stock (in shares)			1	25
Common shares issuable upon conversion of preferred shares (in shares)	10	10	10	10
Shares used in diluted computation (in shares)	19,994	20,493	20,071	20,487
Net income per common share
Basic (in dollars per share)	$ 0.34	$ 0.38	$ 0.94	$ 1.52
Diluted (in dollars per share)	$ 0.34	$ 0.38	$ 0.94	$ 1.52