Note 6 - Stock-based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended	12 Months Ended
	Jun. 30, 2018	Sep. 30, 2017	Sep. 30, 2017
Options outstanding, beginning balance (in shares)	392
Weighted average exercise price per share, beginning balance (in dollars per share)	$ 23.40
Options outstanding, granted (in shares)	44
Exercise price per share, granted (in dollars per share)	$ 29.69
Options outstanding, exercised (in shares)	(42)
Exercise price per share, exercised (in dollars per share)	$ 17.81
Options outstanding, forfeited (in shares)	(9)
Exercise price per share, forfeited (in dollars per share)	$ 29.88
Options outstanding, ending balance (in shares)	385	392	392
Weighted average exercise price per share, ending balance (in dollars per share)	$ 24.59	$ 23.40	$ 23.40
Contractual term - weighted average, ending balance (Year)	7 years 138 days
Aggregate intrinsic value, ending balance	$ 3,565
Options outstanding, vested and anticipated to vest in future (in shares)	383
Weighted average exercise price per share, vested and anticipated to vest in future (in dollars per share)	$ 24.56
Contractual term - weighted average, vested and anticipated to vest in future (Year)	7 years 138 days
Aggregate intrinsic value, vested and anticipated to vest in future	$ 3,548
Options outstanding, exercisable (in shares)	201
Weighted average exercise price per share, exercisable (in dollars per share)	$ 21.04
Contractual term - weighted average, exercisable (Year)	6 years 87 days
Aggregate intrinsic value, exercisable	$ 2,540
Minimum [Member]
Exercise price per share, beginning balance (in dollars per share)	$ 10.23	$ 9.16
Exercise price per share, granted (in dollars per share)	29.69
Exercise price per share, exercised (in dollars per share)	9.16
Exercise price per share, forfeited (in dollars per share)	23.95
Maximum [Member]
Exercise price per share, ending balance (in dollars per share)	37.06		$ 37.06
Exercise price per share, granted (in dollars per share)	29.69
Exercise price per share, exercised (in dollars per share)	23.95
Exercise price per share, forfeited (in dollars per share)	$ 37.06