Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2017

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 six months ended June 30, 2017:



	Options		Weighted Average Exercise Price		Weighted Average Remaining Contractual Life	Aggregate Intrinsic value (in thousands)
Outstanding at December 31, 2016	1,098,823		$	35.39	4.3	$	52,332
Granted	64,507		87.05			287
Exercised	(120,577	)	22.21			7,388
Canceled	(471	)	83.14			4
Outstanding at June 30, 2017	1,042,282		40.09		4.3	53,581
Exercisable at June 30, 2017	851,494		31.93		3.6	50,722

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:



	Six Months Ended June 30,
	2017		2016
Dividend yield	0.23	%	0.26	%
Risk-free interest rate	2.17	%	1.47	%
Stock price volatility	23.4	%	26.9	%
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 six months ended June 30, 2017:



	Restricted Stock and Units		Incentive Stock Units		Weighted Average Grant Date Fair Value
Outstanding at December 31, 2016	396,295		424,750		$	72.18
Granted	151,655		155,575		86.64
Vested	(130,098	)	(153,271	)	70.05
Adjustment for incentive stock awards expected to vest	—		(26,586	)	69.74
Canceled	(4,103	)	(2,458	)	77.20
Outstanding at June 30, 2017	413,749		398,010