CAPITAL STOCK AND SHARE-BASED COMPENSATION (Tables)

12 Months Ended

Dec. 31, 2020

Share-based Payment Arrangement [Abstract]

Schedule of Employee Stock Purchase Plan Activity

The following is a detail of the purchases that were made under the plan:

Employee Stock Purchase Plan Period	Shares Issued	Price
2018 and Prior	3,122,983	$	15.92
January 1, 2019 to March 31, 2019	7,181	104.77
April 1, 2019 to June 30, 2019	8,230	103.20
July 1, 2019 to September 30, 2019	7,216	111.36
October 1, 2019 to December 31, 2019	6,063	141.88
January 1, 2020 to March 31, 2020	5,295	156.01
April 1, 2020 to June 30, 2020	5,414	168.76
July 1, 2020 to September 30, 2020	4,789	200.97
October 1, 2020 to December 31, 2020	4,202	249.33
	3,171,373

Schedule of Share-based Payment Award Valuation Assumptions

The fair values of the awards were estimated using the following assumptions for 2020, 2019 and 2018:

	For the Years Ended December 31,
	2020	2019	2018
Risk Free Rate	0.38% - 1.51%	1.44% - 2.53%	2.56% - 3.04%
Expected Volatility	40.15% - 42.80%	42.46% - 43.83%	42.00% - 45.32%
Expected Term	6.25 years	6.00 - 6.25 years	4.12 - 6.25 years
Weighted Average Fair Value	$86.72	$54.42	$42.48
Dividend Yield	—%	—%	—%

Schedule of Stock Options Activity

The following table presents our stock option activity for 2020:

	Number of Shares	Weighted Average Exercise Price		Weighted Average Contractual Life (Years)
Outstanding options at January 1, 2020	875,974	$	49.62	6.26
Granted	43,249	209.41
Exercised	(622,829)	31.60
Canceled, forfeited or expired	(18,353)	103.89
Outstanding options at December 31, 2020	278,041	$	111.27	7.68
Exercisable options at December 31, 2020	89,429	$	76.40	6.75

The following table presents our non-vested stock option activity for 2020:

	Number of Shares	Weighted Average Grant Date Fair Value
Non-vested stock options at January 1, 2020	305,750	$	41.66
Granted	43,249	86.72
Vested	(142,233)	34.84
Forfeited	(18,154)	47.66
Non-vested stock options at December 31, 2020	188,612	$	56.55

Schedule of Non-Vested Stock Activity

The following table presents our non-vested stock activity for 2020:

	Number of Shares	Weighted Average Grant Date Fair Value
Non-vested stock at January 1, 2020	9,859	$	119.12
Granted	1,560	158.72
Vested	(11,419)	124.53
Canceled, forfeited or expired	—	—
Non-vested stock at December 31, 2020	—	$	—

Schedule of Non-Vested Stock Unit Activity

The following table presents our service-based non-vested stock units activity for 2020:

	Number of  Shares	Weighted Average Grant Date Fair Value
Non-vested stock units at January 1, 2020	231,418	$	91.87
Granted	34,429	206.10
Vested	(89,074)	78.15
Canceled, forfeited or expired	(19,227)	97.36
Non-vested stock units at December 31, 2020	157,546	$	123.92

Schedule of Non-Vested Performance-based Units Activity

The following table presents our performance-based non-vested stock units activity for 2020:

	Number of  Shares	Weighted Average Grant Date Fair Value
Non-vested stock units at January 1, 2020	207,424	$	97.55
Granted	85,727	201.90
Vested	(78,856)	83.12
Canceled, forfeited or expired	(18,008)	101.40
Non-vested stock units at December 31, 2020	196,287	$	148.16