Stock Compensation Plans (Tables)

12 Months Ended

Dec. 31, 2017

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, 2017, 2016, and 2015 valued using the Black-Scholes option valuation model, we used the following assumptions:

	Years ended December 31,
	2017		2016		2015
Risk-free interest rate	1.88% - 2.02%		1.06% - 1.57%		0.80% - 1.21%
Expected dividend yield	—	%	—	%	—	%
Expected option life	5 years		4 years		3 years
Expected volatility	45.2	%	45.0% - 47.0%		42.3% - 48.5%
Weighted-average expected volatility	45.2	%	46.1	%	43.5	%

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, 2017
Outstanding at January 1, 2017	1,090,160		$	48.02
Granted	267,794		34.75
Forfeited	(84,591	)	44.39
Exercised	(96,212	)	37.05
Unearned performance-based options	(20,388	)	59.97
Outstanding at December 31, 2017	1,156,763		$	45.93	4.3	$	7,082
Options exercisable at December 31, 2017	914,941		$	42.20	2.3	$	2,369

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, 2017:

	Shares		Weighted-Average Grant Date Fair Value
Non-vested at January 1, 2017	150,682		$	33.39
Granted	155,975		35.79
Forfeited	(26,855	)	33.95
Vested	(21,706	)	34.55
Unearned performance-based awards	(604	)	52.83
Non-vested at December 31, 2017	257,492		$	34.75

Performance Shares

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

Schedule of Valuation Assumptions

The assumptions used to estimate the fair value of the performance-based stock options and restricted stock units granted during 2015 and valued under the Monte Carlo Simulation model were as follows:

	Years Ended December 31,
	2017		2016		2015
Risk-free interest rate	—	%	—	%	0.95% - 1.48%
Expected dividend yield	—	%	—	%	—	%
Expected option life	—		—		4 years
Expected volatility	—	%	—	%	44.5	%
Weighted-average expected volatility	—	%	—	%	44.5	%