Note 4 - Earnings Per Share - Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Net income	$ 9,718	$ 3,860	$ 11,586	$ 6,057
Weighted average number of shares of common stock outstanding (in shares)	22,493,341	22,413,055	22,482,285	22,399,665
Effect of dilutive securities (in shares)	50,088	148,770	60,034	180,068
Weighted average number of shares of common stock outstanding including effect of dilutive securities (in shares)	22,543,429	22,561,825	22,542,319	22,579,733
Basic earnings per share (in dollars per share)	$ 0.43	$ 0.17	$ 0.52	$ 0.27
Diluted earnings per share (in dollars per share)	$ 0.43	$ 0.17	$ 0.51	$ 0.27