Note 6 - Changes in Shareholders' Equity - Schedule of Changes in Shareholders' Equity (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Balance		$ 141,281			$ 141,281
Net income	$ 6,349		$ 8,412		10,777	$ 16,180
Balance	141,487				141,487
Common Stock [Member]
Balance	20	20	20	$ 20	20	20
Share based compensation	0	0	0	0
Dividends declared	0	0	0	0
Net income	0	0	0	0
Shares Issued	1
Balance	21	20	20	20	21	20
Additional Paid-in Capital [Member]
Balance	7,829	7,111	4,544	3,804	7,111	3,804
Share based compensation	882	718	773	740
Dividends declared	0	0	0	0
Net income	0	0	0	0
Shares Issued
Balance	8,711	7,829	5,317	4,544	8,711	5,317
Retained Earnings [Member]
Balance	132,489	134,141	128,298	126,177	134,141	126,177
Share based compensation	0	0	0	0
Dividends declared	(6,092)	(6,080)	(5,647)	(5,647)
Net income	6,349	4,428	8,412	7,768
Shares Issued
Balance	$ 132,746	$ 132,489	$ 131,063	$ 128,298	$ 132,746	$ 131,063