Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2020

Share-based Payment Arrangement [Abstract]

Summary of Stock Option Activity

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, 2020
Outstanding at December 31, 2017	472,156	$	30.41
Exercised	(54,575)	21.45
Outstanding at December 31, 2018	417,581	$	31.58
Exercised	(211,057)	14.65
Outstanding at December 31, 2019	206,524	$	48.88
Exercised	(134,930)	35.26
Outstanding at December 31, 2020	71,594	$	74.54	4.61	$1,823
Vested and Expected to Vest	71,594	$	74.54	4.61	$1,823
Ending Exercisable	71,594	$	74.54	4.61	$1,823

Schedule of Stock Options Outstanding and Exercisable

A summary of stock options outstanding and exercisable as of December 31, 2020, is as follows:

	Options Outstanding				Options Exercisable
Exercise Price	Shares	Weighted Average Remaining Contractual Life	Weighted Average Exercise Price		Shares	Weighted Average Exercise Price
$47.50 - $47.50	2,700	3.13	$	47.50	2,700	$	47.50
$65.36 - $65.36	1,582	4.15	65.36		1,582	65.36
$65.45 - $65.45	2,900	4.13	65.45		2,900	65.45
$73.52 - $73.52	50,000	4.58	73.52		50,000	73.52
$85.99 - $85.99	14,412	5.15	85.99		14,412	85.99
	71,594	4.61	$	74.54	71,594	$	74.54

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, 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
Granted	109,081	101.52
Released	(110,724)	79.58
Cancelled	(8,863)	90.11
Unreleased at December 31, 2019	212,608	$	91.62
Granted	95,671	98.81
Released	(94,164)	89.43
Cancelled	(5,083)	93.16
Unreleased at December 31, 2020	209,032	$	95.86

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, 2017	30,071	$	83.84
Granted	28,735	96.19
Unvested at December 31, 2018	58,806	$	89.87
Granted	49,334	103.18
Unvested at December 31, 2019	108,140	$	95.94
Granted	45,242	129.38
Released	(47,516)	$	112.16
Unvested at December 31, 2020	105,866	$	102.95

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

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,
	2020	2019	2018
Intrinsic value	$12,266	$6,211	$5,321
Risk-free rate	1.42%	2.53%	2.37%
Volatility	18.4%	20.7%	22.6%
Expected term (in years)	2.9	2.8	2.9
Dividend yield	—%	—%	—%
Unrecognized compensation cost	$6,406	$4,315	$2,739
Term over which compensation cost recognized (in years)	3	3	3