Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Schedule of Equity-Based Compensation Plans

Information related to the Company’s equity-based compensation plans in effect as of December 31, 2023 was as follows:

Plan Category	Number of Securities to be Issued Upon Exercise of Outstanding Options or Vesting of Share Awards		Weighted-Average Exercise Price of Outstanding Options		Number of Securities Remaining Available for Future Issuance Under Equity Compensation Plans
Equity compensation plans approved by security holders		977,549	$	82.00		1,471,786
Equity compensation plans not approved by security holders		—		—		—
		977,549	$	82.00		1,471,786

Schedule of Stock Based Compensation Expense

Total stock-based compensation expense was as follows (in millions):

	Year Ended December 31,						(transition period) Three Months Ended December 31,			Year Ended September 30,
	2023			2022			2021			2021
Stock options	$	—		$	0.3		$	0.2		$	1.8
Stock awards (shares and units)		24.9			25.7			3.5			19.3
Performance share awards		7.0			2.6			0.5			6.1
Cash-settled stock appreciation rights		0.2			(0.8	)		0.3			1.1
Cash-settled restricted stock unit awards		0.7			0.9			0.4			1.5
Total stock-based compensation cost		32.8			28.7			4.9			29.8
Income tax benefit recognized for stock-based compensation		(4.4	)		(4.2	)		(0.8	)		(4.4	)
Stock-based compensation cost, net of tax	$	28.4		$	24.5		$	4.1		$	25.4

Schedule of Stock Option Activity

Stock Options — A summary of the Company’s stock option activity is as follows:

	Year Ended December 31,										(transition period) Three Months Ended December 31,					Year Ended September 30,
	2023					2022					2021					2021
	Options			Weighted- Average Exercise Price		Options			Weighted- Average Exercise Price		Options			Weighted- Average Exercise Price		Options			Weighted- Average Exercise Price
Outstanding, beginning of period		376,769		$	79.86		433,026		$	78.37		471,676		$	77.96		1,083,402		$	74.38
Granted		—			—		—			—		—			—		—			—
Forfeited		—			—		(4,170	)		90.28		(2,002	)		85.04		(8,065	)		81.40
Expired		(9,218	)		83.55		(4,583	)		84.67		—			—		(3,999	)		86.59
Exercised		(122,128	)		75.28		(47,504	)		64.90		(36,648	)		72.69		(599,662	)		71.38
Outstanding, end of period		245,423		$	82.00		376,769		$	79.86		433,026		$	78.37		471,676		$	77.96
Exercisable, end of period		245,423		$	82.00		376,769		$	79.86		364,403		$	76.13		251,049		$	74.73

Schedule of Outstanding Stock Options

Stock options outstanding and exercisable as of December 31, 2023 were as follows (in millions, except share and per share amounts):

Exercise Prices	Options		Weighted Average Remaining Contractual Life (in years)		Weighted Average Exercise Price		Aggregate Intrinsic Value
$60.01 - $80.00		76,831		4.9	$	66.09	$	3.3
$80.01 - $100.00		168,592		5.3	$	89.25		3.2
		245,423		5.2	$	82.00	$	6.5

Schedule of Nonvested Stock Activity

Stock Awards — A summary of the Company’s stock award activity is as follows:

	Year Ended December 31,										(transition period) Three Months Ended December 31,					Year Ended September 30,
	2023					2022					2021					2021
	Number of Shares			Weighted- Average Grant Date Fair Value		Number of Shares			Weighted- Average Grant Date Fair Value		Number of Shares			Weighted- Average Grant Date Fair Value		Number of Shares			Weighted- Average Grant Date Fair Value
Nonvested, beginning of period		363,661		$	103.86		308,941		$	90.10		394,888		$	81.58		346,808		$	79.44
Granted		344,484			90.91		255,375			109.66		63,800			114.89		307,025			82.80
Forfeited		(43,602	)		97.85		(26,020	)		97.24		(4,428	)		86.08		(36,545	)		78.81
Vested		(202,114	)		95.85		(174,635	)		88.98		(145,319	)		77.97		(222,400	)		80.39
Nonvested, end of period		462,429		$	98.28		363,661		$	103.86		308,941		$	90.10		394,888		$	81.58

Schedule of Nonvested Performance-Based Units Activity

Performance Share Awards — A summary of the Company’s performance share awards activity is as follows. There was no activity related to performance share awards during the three months ended December 31, 2021:

	Year Ended December 31,										Year Ended September 30,
	2023					2022					2021
	Number of Shares			Weighted- Average Grant Date Fair Value		Number of Shares			Weighted- Average Grant Date Fair Value		Number of Shares			Weighted- Average Grant Date Fair Value
Nonvested, beginning of period		97,600		$	108.20		72,475		$	93.62		110,450		$	89.54
Granted		81,208			100.08		57,250			126.60		86,550			86.09
Forfeited		(9,733	)		111.50		(3,748	)		114.83		(52,099	)		90.03
Performance adjustments		8,479			81.06		369			107.45		63,843			80.45
Vested		(53,595	)		85.90		(28,746	)		103.47		(136,269	)		80.73
Nonvested, end of period		123,959		$	110.40		97,600		$	108.20		72,475		$	93.62

Schedule of Weighted-Average Assumptions to Estimate Grant Date Fair Values

The grant date fair values of the TSR performance share awards were estimated using a Monte Carlo simulation model utilizing the following weighted-average assumptions:

	Year Ended December 31,						Year Ended September 30,
Total Shareholder Return Performance Shares Granted During	2023			2022			2021
Assumptions:
Expected term (in years)		2.86			2.86			2.87
Expected volatility		35.45	%		38.52	%		40.33	%
Risk-free interest rate		4.32	%		1.64	%		0.23	%