Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Summary Information for Restricted Stock Awards and Incentive Compensation Stock Awards

The following table summarizes information for restricted stock awards and incentive compensation stock awards for 2023:

	Restricted Stock - Service Based					Restricted Stock - Performance Based					Incentive Compensation Stock
	Number of Awards			Weighted- Average Grant-Date Fair Value		Number of Awards			Weighted- Average Grant-Date Fair Value		Number of Awards			Weighted- Average Grant-Date Fair Value
January 1, 2023		215,644		$	272.86		103,795		$	339.17		32,149		$	341.72
Awarded		60,982		$	369.18		33,103		$	392.73		4,012		$	362.08
Distributed		(59,184	)	$	305.80		(70,370	)	$	266.97		(18,835	)	$	325.48
Forfeited		(6,799	)	$	341.96		(1,626	)	$	371.00		—		$	—
Adjustment for performance		—		$	—		33,248		$	266.97		—		$	—
December 31, 2023		210,643		$	289.26		98,150		$	384.02		17,326		$	364.09

Summary Information for Stock Options

The following table includes summary information for stock options as of December 31, 2023:

	Number of Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Life (years)
Outstanding at January 1, 2023		15,283		$	136.55
Exercised		(9,180	)	$	131.50
Outstanding at December 31, 2023		6,103		$	144.14		1.1
Exercisable at December 31, 2023		6,103		$	144.14		1.1

Schedule of Stock-Based Compensation Expense

The following table summarizes stock-based compensation expense for the years ended December 31, 2023, 2022 and 2021, unrecognized compensation cost for nonvested awards at December 31, 2023 and the weighted-average period over which unrecognized compensation cost will be recognized:

(in millions, except year data)	Restricted Stock		Incentive Compensation Stock		Directors’ Fees Paid in Stock		Total
Stock-based compensation expense recognized for    years ended December 31:
2023	$	48.7	$	0.8	$	0.5	$	50.0
2022	$	41.0	$	1.1	$	0.6	$	42.7
2021	$	41.4	$	1.0	$	0.6	$	43.0
Unrecognized compensation cost at    December 31, 2023	$	39.5	$	0.4	$	—	$	39.9
Weighted-average period over which unrecognized    compensation cost will be recognized	1.8 years		1.3 years

Stock-Based Compensation Expense in Future for Outstanding Awards

The following presents expected stock-based compensation expense in future periods for outstanding awards as of December 31, 2023:

(in millions)
2024	$	28.2
2025		9.1
2026		1.8
2027		0.7
2028		0.1
Total	$	39.9