Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2020

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, 2020, 2019 and 2018:

	Year Ended December 31,
	2020			2019			2018
Expected life (in years)		6.7			6.6			6.2
Interest rate		1.67	%		2.62	%		2.50	%
Volatility		30.34	%		30.26	%		30.33	%
Expected dividend yield		0.35	%		0.37	%		0.26	%

Stock Option Activity

The following table summarizes stock option activity for the year ended December 31, 2020:

	Awards			Weighted Average Exercise Price per Share		Weighted Average Remaining Contractual Life (Years)		Aggregate Intrinsic Value (Millions)
Awards outstanding at December 31, 2019		1,227,620		$	55.83
Granted		286,078			57.67
Exercised		(93,099	)		35.11
Canceled		(57,233	)		63.92
Awards outstanding at December 31, 2020		1,363,366		$	57.29		6.15		$	11.4
Awards exercisable at December 31, 2020		876,206		$	56.55		4.83		$	8.9

Non-vested Stock Option Activity

Non-vested stock option activity for the year ended December 31, 2020 is as follows:

	Awards			Weighted Average Grant Date Fair Value per Share
Nonvested awards outstanding at December 31, 2019		438,773		$	63.15
Granted		286,078			57.67
Vested		(199,723	)		66.94
Canceled		(37,968	)		60.15
Nonvested awards outstanding at December 31, 2020		487,160		$	58.61

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, 2019		177,736		$	62.40
Granted		108,212			56.93
Vested		(43,702	)		66.07
Canceled		(40,261	)		65.42
Unvested balance at December 31, 2020		201,985		$	58.07