Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

The following table summarizes the Company’s stock option activity and related information for the 2011 Plan, the 2000 Plan and the Directors Plan for the three months ended March 31, 2018:



	Options		Weighted Average Exercise Price		Weighted Average Remaining Contractual Life	Aggregate Intrinsic value (in thousands)
Outstanding at December 31, 2017	983,512		$	40.62	4.0	$	40,137
Granted	62,020		71.79			596
Exercised	(154,418	)	18.32			9,741
Canceled	(12,866	)	67.61			117
Outstanding at March 31, 2018	878,248		46.34		4.7	30,791
Exercisable at March 31, 2018	711,207		39.62		4.1	29,714

Share-Based Fair Value of Each Option Grant Weighted-Average Assumptions

The fair value of each option grant is estimated on the date of grant using the Black-Scholes option pricing model with the following weighted-average assumptions:



	Three Months Ended March 31,
	2018		2017
Dividend yield	0.33	%	0.23	%
Risk-free interest rate	2.70	%	2.17	%
Stock price volatility	23.9	%	23.4	%
Expected life (years)	5.0		5.0

Restricted Stock Activity and Incentive Stock Awards Activity

The following table summarizes the restricted stock activity and related information for the 2011 Plan, the 2000 Plan and the Directors Plan, and incentive stock units activity for the 2011 Plan and the 2000 Plan with related information for the three months ended March 31, 2018:



	Restricted Stock and Units		Incentive Stock Units		Weighted Average Grant Date Fair Value
Outstanding at December 31, 2017	399,000		327,333		$	78.76
Granted	188,570		172,400		71.79
Vested	(104,405	)	(93,312	)	81.61
Adjustment for incentive stock awards expected to vest	—		26,056		77.72
Canceled	(10,367	)	(13,600	)	76.92
Outstanding at March 31, 2018	472,798		418,877