Note 9 - Net Income Per Share - Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2020
Net income	$ 6,066	$ 4,257	$ 6,349	$ 4,428	$ 6,812	$ 7,611	$ 8,412	$ 7,768	$ 21,100	$ 30,603	$ 25,851
Basic (in shares)									20,176	20,060	20,041
Common shares issuable upon the vesting of restricted stock (in shares)									172	49	4
Common shares issuable upon conversion of preferred shares (in shares)									10	10	10
Shares used in diluted computation (in shares)									20,358	20,119	20,055
Basic (in dollars per share)									$ 1.05	$ 1.53	$ 1.29
Diluted (in dollars per share)	$ 0.30	$ 0.21	$ 0.31	$ 0.22	$ 0.34	$ 0.38	$ 0.42	$ 0.39	$ 1.04	$ 1.52	$ 1.29