Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [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 2020:

	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, 2020		183,939		$	185.06		124,221		$	204.21		39,584		$	198.83
Awarded		92,472		$	222.39		38,272		$	266.97		21,082		$	258.67
Distributed		(66,797	)	$	194.94		(79,192	)	$	211.29		(17,354	)	$	209.99
Forfeited		(2,633	)	$	206.08		(1,367	)	$	216.39		(689	)	$	201.43
Adjustment for performance		—		$	—		36,642		$	211.29		—		$	—
December 31, 2020		206,981		$	198.28		118,576		$	228.15		42,623		$	223.85

Summary Information for Stock Options

The following table includes summary information for stock options as of December 31, 2020:

	Number of Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Life (years)
Outstanding at January 1, 2020		58,840		$	108.93
Exercised		(27,401	)	$	86.89
Terminated		(350	)	$	51.64
Outstanding at December 31, 2020		31,089		$	129.00		3.5
Exercisable at December 31, 2020		31,089		$	129.00		3.5

Schedule of Stock-Based Compensation Expense

The following table summarizes stock-based compensation expense for the years ended December 31, 2020, 2019 and 2018, unrecognized compensation cost for nonvested awards at December 31, 2020 and the weighted-average period over which unrecognized compensation cost will be recognized:

(in millions, except year data)	Stock Options		Restricted Stock		Incentive Compensation Stock		Directors’ Awards		Total
Stock-based compensation expense recognized for    years ended December 31:
2020	$	—	$	28.5	$	0.8	$	0.7	$	30.0
2019	$	0.1	$	32.6	$	0.8	$	0.6	$	34.1
2018	$	0.3	$	27.7	$	0.7	$	0.6	$	29.3
Unrecognized compensation cost at    December 31, 2020	$	—	$	25.6	$	0.7	$	—	$	26.3
Weighted-average period over which unrecognized    compensation cost will be recognized			2.4 years		1.7 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, 2020:

(in millions)
2021	$	15.8
2022		7.0
2023		1.7
2024		1.3
2025		0.5
Total	$	26.3