Note 6 - Changes in Shareholders' Equity - Schedule of Changes in Shareholders' Equity (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2019	Jun. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Balance		$ 130,010			$ 130,010
Net income	$ 8,412		$ 6,665		16,180	$ 12,008
Repurchase and retirement of common stock						(11,500)
Balance	136,409				136,409
Additional Paid-in Capital [Member]
Balance	4,544	3,804	1,617	$ 12,478	3,804	12,478
Share based compensation	773	740	730	635
Dividends declared	0	0	0	0
Net income	0	0	0	0
Repurchase and retirement of common stock				(11,496)
Balance	5,317	4,544	2,347	1,617	5,317	2,347
Retained Earnings [Member]
Balance	128,298	126,177	121,997	122,172	126,177	122,172
Share based compensation	0	0	0	0
Dividends declared	(5,647)	(5,647)	(5,447)	(5,518)
Net income	8,412	7,768	6,665	5,343
Repurchase and retirement of common stock				0
Balance	$ 131,063	$ 128,298	$ 123,215	$ 121,997	$ 131,063	$ 123,215