Stock Compensation Plans (Tables)

12 Months Ended

Dec. 31, 2018

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

Schedule of Valuation Assumptions

For stock options granted during the years ended December 31, 2018, 2017, and 2016 valued using the Black-Scholes option valuation model, we used the following assumptions:

	Years ended December 31,
	2018		2017		2016
Risk-free interest rate	2.65	%	1.88% - 2.02%		1.06% - 1.57%
Expected dividend yield	—	%	—	%	—	%
Expected option life	4 years		5 years		4 years
Expected volatility	45	%	45.2	%	45.0% - 47.0%
Weighted-average expected volatility	45.0	%	45.2	%	46.1	%

Schedule of Stock Option Activity and Weighted Average Exercise Prices

A summary of stock option activity and weighted average exercise prices follows:

	Options		Weighted- Average Exercise Price		Weighted-Average Remaining Contractual Term (Years)	Aggregate Intrinsic Value as of December 31, 2018
Outstanding at January 1, 2018	1,156,763		$	45.93
Granted	174,439		61.30
Forfeited	(81,222	)	51.66
Exercised	(439,877	)	47.21
Unearned performance-based options	(17,160	)	59.97
Outstanding at December 31, 2018	792,943		$	47.59	4.4	$	2,160
Options exercisable at December 31, 2018	427,006		$	48.84	2.1	$	862

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 year ended December 31, 2018:

	Shares		Weighted-Average Grant Date Fair Value
Non-vested at January 1, 2018	257,492		$	34.75
Granted	102,458		60.26
Forfeited	(29,692	)	39.36
Vested	(18,618	)	35.03
Unearned performance-based awards	(640	)	51.15
Non-vested at December 31, 2018	311,000		$	42.66