Note 9 - Shareholders' Equity - Black-scholes Option Valuation Assumptions (Details) - $ / shares	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Number of options granted (in shares)	19,100	8,200	19,900	10,200
Volatility	80.39%	84.71%	80.52%	84.60%
Estimated life (years) (Year)	6 years	6 years	6 years	6 years
Risk-free interest rate	2.52%	2.02%	2.50%	1.99%
Weighted-average fair value per share of grants (in dollars per share)	$ 1.72	$ 2.29	$ 1.73	$ 2.20