Stock-based Compensation (Tables)

6 Months Ended

Jun. 30, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Compensation Cost and Related Tax Benefits

Compensation cost for the Company’s stock-based awards and the related tax benefits were as follows:

	Three Months Ended June 30,						Six Months Ended June 30,
(in millions)	2017			2016			2017			2016
Stock-based compensation expense	$	4.1		$	2.7		$	7.3		$	5.5
Tax benefit		(1.4	)		(0.9	)		(2.5	)		(1.9	)
Stock-based compensation expense, net of taxes	$	2.7		$	1.8		$	4.8		$	3.6

Summary of Stock Option Plan Activity

Information on the Company’s stock option plans is summarized below.

	Six Months Ended June 30,
	2017					2016
(in whole shares and dollars)	Shares			Weighted Average Exercise Price		Shares			Weighted Average Exercise Price
Outstanding, beginning of period		1,396,152		$	68.63		1,619,948		$	56.57
Granted		460,610			90.85		524,940			82.74
Exercised		(180,940	)		59.50		(495,242	)		48.57
Forfeited or cancelled		(16,567	)		80.40		(161,207	)		66.80
Outstanding, end of period		1,659,255			75.68		1,488,439			67.36

Summary of Restricted Stock Activity

The following tables summarize activity information about employee restricted stock units:

	Six Months Ended June 30,
	2017					2016
(in whole shares and dollars)	Shares			Weighted Average Grant Date Fair Value		Shares			Weighted Average Grant Date Fair Value
Time-based restricted stock units:
Outstanding, beginning of period		269,063		$	73.91		301,897		$	54.54
Granted		128,235			90.51		141,949			83.47
Vested		(70,590	)		59.29		(135,863	)		42.44
Forfeited		(13,830	)		84.30		(18,831	)		67.15
Outstanding, end of period		312,878			83.55		289,152			73.61
Performance-based and market-based restricted stock units:
Outstanding, beginning of period		115,057		$	78.82		196,142		$	47.89
Granted		60,101			79.48		118,736			73.14
Vested		(17,642	)		58.16		(144,141	)		41.11
Forfeited		(2,180	)		95.36		(56,500	)		63.52
Outstanding, end of period		155,336			81.19		114,237			74.97