Note 3 - Stock-based Compensation (Tables)

12 Months Ended

Sep. 30, 2022

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
Nonvested at September 30, 2021		312,596		$	74.33
Granted		128,396		$	67.43
Vested		(91,111	)	$	79.40
Forfeited		(6,357	)	$	69.43
Nonvested at September 30, 2022		343,524		$	70.14

				Weighted
				Average
				Grant Date
	Shares/			Fair Value
	Units			Per Share
Nonvested at September 30, 2021		110,300		$	70.98
Granted		62,945		$	63.57
Vested		(46,970	)	$	72.67
Forfeited		(4,030	)	$	68.62
Nonvested at September 30, 2022		122,245		$	66.60

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

	2022		2021		2020
Risk-free interest rate		0.79%		0.22%		1.57%
Expected dividend yield of stock		—		—		—
Expected volatility of stock		32.2%		31.4%		16.8%
Vesting period (in years)		3.0		3.0		3.0

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

	2022			2021			2020
Total compensation cost	$	7.5		$	16.6		$	9.4
Compensation cost capitalized		(1.1	)		(2.7	)		(0.6	)
Compensation cost recognized in net income		6.4			13.9			8.8
Income tax benefit recognized in net income		(1.5	)		(3.2	)		(2.1	)
Compensation cost recognized in net income, net of income tax	$	4.9		$	10.7		$	6.7