Stock-Based Compensation - (Tables)

12 Months Ended

Dec. 31, 2017

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

A summary of stock option activity is as follows:



Options	Number of Shares		Weighted Average Exercise Price		Weighted Average Remaining Contractual Life (Years)	Aggregate Intrinsic Value as of December 31, 2017
Outstanding at December 31, 2014	568,727		$	16.62
Granted	89,575		69.93
Exercised	(79,974	)	18.79
Forfeited	(5,699	)	39.83
Outstanding at December 31, 2015	572,629		$	24.42
Granted	35,800		85.99
Exercised	(97,855	)	14.75
Forfeited	—		—
Outstanding at December 31, 2016	510,574		$	30.60
Exercised	(38,418	)	32.94
Outstanding at December 31, 2017	472,156		$	30.41	3.71	$26,934
Vested and Expected to Vest	468,601		$	30.05	3.68	$26,897
Ending Exercisable	394,363		$	21.86	2.96	$25,864

Schedule of Weighted Average Assumptions Used to Estimate Fair Value of Granted Stock Options

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:



	For the Year Ended December 31,
	2016		2015
Expected volatility	37.0	%	38.0	%
Dividend yield	3.6	%	3.6	%
Risk-free interest rate	1.3	%	1.5	%
Average expected term (years)	5		5

Schedule of Stock Options Outstanding and Exercisable

A summary of stock options outstanding and exercisable as of December 31, 2017, is as follows:



	Options Outstanding				Options Exercisable
Exercise Price	Shares	Weighted Average Remaining Contractual Life	Weighted Average Exercise Price		Shares	Weighted Average Exercise Price
$6.22 - $6.22	157,750	1.13	$	6.22	157,750	$	6.22
$11.59 - $12.21	105,480	2.17	12.04		105,480	12.04
$19.6 - $65.36	105,986	5.20	39.89		89,629	36.47
$65.45 - $73.52	67,140	7.47	71.46		32,550	71.65
$85.99 - $85.99	35,800	8.15	85.99		8,954	85.99
$6.22-$85.99	472,156	3.71	$	30.41	394,363	$	21.86

Summary of Company's Employee and Director Share Grant Activity

A summary of the Company’s employee and director share grant activity is as follows:



Restricted Stock Grants	Shares		Weighted-Average Grant-Date Fair Value
Unreleased at December 31, 2014	291,749		$	37.73
Granted	174,558		69.18
Released	(129,808	)	34.86
Cancelled	(18,090	)	44.54
Unreleased at December 31, 2015	318,409		$	55.75
Granted	119,931		87.61
Released	(128,808	)	50.05
Cancelled	(9,947	)	67.36
Unreleased at December 31, 2016	299,585		$	70.57
Granted	95,392		74.49
Released	(120,323	)	63.95
Cancelled	(8,179	)	77.25
Unreleased at December 31, 2017	266,475		$	74.76

Schedule of Nonvested Performance-based Units Activity

A summary of the PSU activity is as follows:



Performance-based Stock Units	Units	Weighted-Average Grant-Date Fair Value
Unvested at December 31, 2016	—	$	—
Granted	30,071	83.84
Unvested at December 31, 2017	30,071	83.84