Stock-Based Compensation - (Tables)

12 Months Ended

Dec. 31, 2018

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, 2018
Outstanding at December 31, 2015	572,629		$	24.42
Granted	35,800		85.99
Exercised	(97,855	)	14.75
Outstanding at December 31, 2016	510,574		$	30.60
Exercised	(38,418	)	32.94
Outstanding at December 31, 2017	472,156		$	30.41
Exercised	(54,575	)	21.45
Outstanding at December 31, 2018	417,581		$	31.58	2.78	$24,597

Vested and Expected to Vest	416,567		$	31.46	2.77	$24,587
Ending Exercisable	377,292		$	26.72	2.35	$24,057

Schedule of Weighted Average Assumptions Used to Estimate Fair Value of Awards

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
Expected volatility			37.0%
Dividend yield			3.6%
Risk-free interest rate			1.3%
Average expected term (years)			5

The Company estimated the fair value of the PSUs as of the grant date, using the closing trading price of the Company's common stock on the grant date to value the FFO Target portion. A Monte Carlo simulation model was used to calculate the fair value of the TSR Target portion of the PSUs, using the following assumptions:



	For the Year Ended December 31,
	2018	2017
Intrinsic value	$5,321	$2,630
Compensation cost	$1,873	$840
Risk-free rate	2.37%	1.62%
Volatility	22.6%	21.4%
Expected term (in years)	2.9	2.8
Dividend yield	—%	—%
Unrecognized compensation cost	$2,739	$1,681
Term over which unrecognized compensation cost recognized	2	2

Schedule of Stock Options Outstanding and Exercisable

A summary of stock options outstanding and exercisable as of December 31, 2018, 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	139,250	0.13	$	6.22	139,250	$	6.22
$11.59 - $11.59	20,080	1.13	11.59		20,080	11.59
$12.21 - $12.21	77,400	1.18	12.21		77,400	12.21
$19.6 - $28.79	29,469	2.65	23.56		29,469	23.56
$38.4 - $38.4	10,360	4.14	38.4		10,360	38.40
$47.5 - $47.5	17,687	5.13	47.5		17,687	47.50
$65.36 - $65.36	20,395	6.15	65.36		15,297	65.36
$65.45 - $65.45	17,140	6.13	65.45		12,345	65.45
$73.52 - $73.52	50,000	6.58	73.52		37,500	73.52
$85.99 - $85.99	35,800	7.15	85.99		17,904	85.99
	417,581	2.78	$	31.58	377,292	$	26.72

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, 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
Granted	85,066		86.14
Released	(116,656	)	72.38
Cancelled	(11,771	)	80.96
Unreleased at December 31, 2018	223,114		$	80.02

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
Granted	28,735	96.19
Unvested at December 31, 2018	58,806	$	89.87