Note 3 - Stock-based Compensation - Compensation Cost of Share-based Compensation Arrangements (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Total compensation cost	$ 6.6	$ 11.2	$ 7.5
Compensation cost capitalized	(0.8)	(1.4)	(1.1)
Compensation cost recognized in net income	5.8	9.8	6.4
Income tax benefit recognized in net income	(1.3)	(2.2)	(1.5)
Compensation cost recognized in net income, net of income tax	$ 4.5	$ 7.6	$ 4.9