Stock-Based Compensation Plans (Tables)

12 Months Ended

Dec. 31, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation Expense

Total stock-based compensation expense was as follows:

	Year Ended December 31,
	2020		2019		2018
	(In thousands)
Employees:
Restricted stock and performance shares	$	21,310	$	20,182	$	12,559
Stock options		3,100		4,032		2,193
		24,410		24,214		14,752
Non-employee directors:
Restricted stock		1,203		1,080		1,098
Total stock-based compensation	$	25,613	$	25,294	$	15,850

Assumptions Used for the Black-Scholes Option-Pricing Model to Determine the Per Share Weighted Average Fair Value for Options Granted

The following table represents the assumptions used for the Black-Scholes option-pricing model to determine the per share weighted-average fair value for options granted, excluding the two awards discussed below:

	Year Ended December 31,
	2020			2019			2018
Expected life (years)		5.0			5.0			5.0
Risk-free interest rate		1.6	%		2.6	%		2.2	%
Expected volatility		26.8	%		25.9	%		26.9	%
Expected dividend yield		0.6	%		0.8	%		0.8	%

Stock Option Activity

The following table reports stock option activity during the three years ended December 31, 2020 and the intrinsic value as of December 31, 2020:

	Number of Shares			Weighted-Average Exercise Price ($)		Remaining Contractual Term		Intrinsic Value ($)
								(In thousands)
Outstanding at December 31, 2017		529,611			67.60
Granted		168,217			261.19
Canceled		(1,676	)		142.69
Exercised		(120,588	)		24.66
Outstanding at December 31, 2018		575,564			132.93
Granted		82,474			279.57
Canceled		(548	)		198.67
Exercised		(106,899	)		28.24
Outstanding at December 31, 2019		550,591			175.16
Granted		13,900			368.10
Canceled		(218	)		307.52
Exercised		(176,901	)		84.07				76,709
Outstanding at December 31, 2020		387,372			223.60		2.8		134,401
Exercisable at December 31, 2020		99,415			137.78		1.7		43,025

Summary of Performance of Share Activity for Annual Awards

The following table reports performance share activity for the one-year performance awards for the two years ended December 31, 2019:

Performance year:	2019		2018
Target share pay-out		16,716		10,479
Actual share pay-out (paid in following year)		19,401		10,479
Weighted average fair value per share on grant date	$	223.81	$	202.04

Restricted Stock and Performance Share Activity

The following table reports restricted stock and performance share activity during the three years ended December 31, 2020:

	Number of Restricted Shares			Weighted-Average Grant Date Fair Value
Outstanding at December 31, 2017		319,599		$	88.77
Granted		59,179
Performance share pay-out		8,094
Canceled		(4,046	)
Vested		(110,956	)
Outstanding at December 31, 2018		271,870		$	112.47
Granted		118,632
Performance share pay-out		87,163
Canceled		(2,321	)
Vested		(129,312	)
Outstanding at December 31, 2019		346,032		$	154.27
Granted		38,907
Performance share pay-out		19,401
Canceled		(3,480	)
Vested		(170,213	)
Outstanding at December 31, 2020		230,647		$	224.63