Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2018

Stock-Based Compensation [Abstract]

Weighted average assumptions used to determine fair value for stock awards

The fair value for stock awards was estimated at the date of grant using the Black-Scholes option valuation model with the following weighted average assumptions for the years ended December 31, 2018, 2017 and 2016:

	Year Ended December 31,
	2018		2017		2016
Expected life (in years)		6.2		6.4		6.5
Interest rate		2.50%		2.04%		1.72%
Volatility		30.33%		36.61%		36.75%
Expected dividend yield		0.26%		0.26%		0.54%

Summary of stock option activity

The following table summarizes stock option activity for the year ended December 31, 2018:

	Awards			Weighted Average Exercise Price per Share		Weighted Average Remaining Contractual Life (Years)		Aggregate Intrinsic Value (Millions)
Awards outstanding at December 31, 2017		996,839		$	48.21
Granted		191,147			76.09
Exercised		(98,945	)		33.83
Canceled		(34,782	)		65.74
Awards outstanding at December 31, 2018		1,054,259		$	54.04		6.10		$	7.8
Awards exercisable at December 31, 2018		688,652		$	46.17		4.90		$	6.9

Non-vested stock option activity

Non-vested stock option activity for the year ended December 31, 2018 is as follows:

	Awards			Weighted Average Grant Date Fair Value per Share
Nonvested awards outstanding at December 31, 2017		400,393		$	58.94
Granted		191,147			76.09
Vested		(195,055	)		56.17
Canceled		(30,878	)		65.13
Nonvested awards outstanding at December 31, 2018		365,607		$	68.86

Summary of restricted stock activity

The following table summarizes the restricted stock activity for the Plan:

	Awards			Weighted Average Grant Date Fair Value per Share
Unvested balance at December 31, 2017		180,110		$	58.57
Granted		69,361			76.26
Vested		(59,649	)		56.44
Canceled		(55,244	)		58.57
Unvested balance at December 31, 2018		134,578		$	68.64