Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2019

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 2019:

	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, 2019		278,147		$	158.29		151,939		$	174.74		35,376		$	206.55
Awarded		86,922		$	196.91		49,644		$	192.27		21,883		$	192.27
Distributed		(171,689	)	$	148.72		(54,424	)	$	133.73		(15,948	)	$	206.23
Forfeited		(9,441	)	$	166.51		(5,329	)	$	205.21		(1,727	)	$	205.54
Adjustment for performance		—		$	—		(17,609	)	$	133.77		—		$	—
December 31, 2019		183,939		$	185.06		124,221		$	204.21		39,584		$	198.83

Summary Information for Stock Options

The following table includes summary information for stock options as of December 31, 2019:

	Number of Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Life (years)
Outstanding at January 1, 2019		210,390		$	95.93
Exercised		(150,722	)	$	90.86
Terminated		(828	)	$	94.75
Outstanding at December 31, 2019		58,840		$	108.93		3.1
Exercisable at December 31, 2019		58,840		$	108.93		3.1

Schedule of Stock-Based Compensation Expense

The following table summarizes stock-based compensation expense for the years ended December 31, 2019, 2018 and 2017, unrecognized compensation cost for nonvested awards at December 31, 2019 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:
2019	$	0.1	$	32.6	$	0.8	$	0.6	$	34.1
2018	$	0.3	$	27.7	$	0.7	$	0.6	$	29.3
2017	$	0.7	$	28.7	$	0.7	$	0.4	$	30.5
Unrecognized compensation cost at    December 31, 2019	$	—	$	22.7	$	0.5	$	—	$	23.2
Weighted-average period over which unrecognized    compensation cost will be recognized			2.1 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, 2019:

(in millions)
2020	$	14.9
2021		7.2
2022		0.8
2023		0.3
Total	$	23.2