Note 3 - Stock-based Compensation (Tables)

12 Months Ended

Sep. 30, 2023

Notes Tables

Share-Based Payment Arrangement, Restricted Stock and Restricted Stock Unit, Activity [Table Text Block]

				Weighted
				Average
				Grant Date
				Fair Value
	Units			Per Unit
Non-vested at September 30, 2022		343,524		$	70.14
Granted		116,390		$	79.88
Adjusted for performance		(13,459	)	$	76.91
Vested		(74,556	)	$	76.91
Forfeited		(23,546	)	$	71.73
Non-vested at September 30, 2023		348,353		$	71.76

				Weighted
				Average
				Grant Date
	Shares/			Fair Value
	Units			Per Share
Non-vested at September 30, 2022		122,245		$	66.60
Granted		68,244		$	72.60
Vested		(59,040	)	$	75.27
Forfeited		(8,460	)	$	65.36
Non-vested at September 30, 2023		122,989		$	65.85

Schedule of Share-Based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

	2023		2022		2021
Risk-free interest rate		4.26%		0.79%		0.22%
Expected dividend yield of stock		—		—		—
Expected volatility of stock		33.8%		32.2%		31.4%
Performance period (in years)		3.0		3.0		3.0

Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block]

	2023			2022			2021
Total compensation cost	$	11.2		$	7.5		$	16.6
Compensation cost capitalized		(1.4	)		(1.1	)		(2.7	)
Compensation cost recognized in net income		9.8			6.4			13.9
Income tax benefit recognized in net income		(2.2	)		(1.5	)		(3.2	)
Compensation cost recognized in net income, net of income tax	$	7.6		$	4.9		$	10.7