Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

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

Summary of Assumptions for Options Issued

The assumptions for options issued during 2017, 2016, and 2015 are presented below:

	2017		2016		2015
Expected term (in years)	5.3		5.3		4.9
Volatility	24.9	%	29.6	%	25.0	%
Weighted-average risk-free interest rate	1.95	%	1.25	%	1.54	%
Dividend yield	0.60	%	0.80	%	0.76	%

Summary of Options Including Non-Plan Stock Options

A summary of the status of our options (including Non-Plan Stock Options) as of December 31, 2017, and changes during the year, is presented below:

	2017
	Shares	Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (Year)	Aggregate Intrinsic Value (In Thousands)
Stock Options:
Outstanding at beginning of year	1,547,980	$	17.83	3.17	$	44,153
Plus: Granted	45,134	47.05
Less: Exercised	250,975	16.44
Forfeited	3,033	13.68
Outstanding at end of year	1,339,106	19.08		2.56	38,525
Nonvested at end of year	389,134			1.69	9,574
Exercisable at end of year	949,972	17.37		2.26	29,951

Schedule of Nonvested Stock Option Outstanding

The following table provides information about our nonvested stock options outstanding at December 31, 2017:

	2017
	Shares	Weighted- Average Exercise Price		Weighted- Average Grant Date Fair Value
Stock Options:
Nonvested at beginning of period	704,421	$	19.08	$	5.23
Plus: Granted	45,134	47.05		11.50
Less: Vested	359,671	18.08		4.92
Forfeited	750	15.83		3.44
Nonvested at end of period	389,134	23.25		6.24

Schedule of RSAs and RSUs

The following table summarizes the Company’s RSAs and RSUs, including performance awards, and changes during the year:

	Units (in whole)	Weighted Average Grant-Date Fair Value per Unit
Balance at December 31, 2016	135,592	$	25.33
Plus: Granted	36,573	47.05
Less: Vested	55,444	22.90
Forfeited	2,333	29.53
Balance at December 31, 2017	114,388	35.54