Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2018

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Schedule of Stock Option Activity and Weighted Average Exercise Prices

A summary of stock option activity and weighted-average exercise prices during the six months ended June 30, 2018 follows:

	Options		Weighted- Average Exercise Price		Weighted-Average Remaining Contractual Term (Years)	Aggregate Intrinsic Value as of June 30, 2018
Outstanding at January 1, 2018	1,156,763		$	45.93
Granted	174,439		61.30
Forfeited or expired	(60,448	)	50.21
Exercised	(162,594	)	43.41
Unearned performance-based options	(17,160	)	59.97
Outstanding at June 30, 2018	1,091,000		$	48.19	4.4	$	9,585
Options exercisable at June 30, 2018	918,462		$	42.24	2.4	$	4,689

Schedule of Restricted Stock and Restricted Stock Units Activity and Weighted-Average Grant Date Fair Value

The following table summarizes the restricted stock and restricted stock unit activity and weighted average grant-date fair values for the six months ended June 30, 2018:

	Shares		Weighted-Average Grant Date Fair Value
Non-vested at January 1, 2018	257,492		$	34.75
Granted	98,448		60.29
Forfeited	(17,748	)	37.59
Vested	(18,618	)	35.03
Unearned performance-based awards	(640	)	51.15
Non-vested at June 30, 2018	318,934		$	42.41

Employee Stock Option

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Schedule of Valuation Assumptions

For stock options granted during the six months ended June 30, 2018 and June 30, 2017 valued using the Black-Scholes option valuation model, we used the following assumptions:

	Six Months Ended
	June 30, 2018		June 30, 2017
Risk-free interest rate	2.65	%	1.88% - 2.02%
Expected dividend yield	—	%	—	%
Expected term of option	4 years		5 years
Expected volatility	45.0	%	45.2	%
Weighted-average expected volatility	45.0	%	45.2	%