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, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Net income	$ 7,787	$ 9,064	$ 31,121	$ 27,100
Weighted average number of common shares outstanding used in basic computation (in shares)	20,483	20,368	20,452	20,337
Common shares issuable upon vesting of restricted stock (in shares)		47	25	90
Common shares issuable upon conversion of preferred shares (in shares)	10	10	10	10
Shares used in diluted computation (in shares)	20,493	20,425	20,487	20,437
Basic (in dollars per share)	$ 0.38	$ 0.45	$ 1.52	$ 1.33
Diluted (in dollars per share)	$ 0.38	$ 0.44	$ 1.52	$ 1.33