Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2021

Share-based Payment Arrangement [Abstract]

Summary of Expense Related to Share-Based Payments

The table below summarizes the expense related to share-based payments recognized in the three months ended March 31 (in thousands):

 

	Three Months Ended March 31,
	2021		2020
Stock options	$	4,590	$	7,020
Restricted stock	13,157		7,155
Stock-based compensation	$	17,747	$	14,175

Summary of Total Unrecognized Compensation Cost Related to Stock-Based Compensation

The following table summarizes the Company’s total unrecognized compensation cost related to stock-based compensation as of March 31, 2021 (cost in thousands):

	Unrecognized Compensation Cost		Weighted Average Period of Expense Recognition (in Years)
Stock options	$	41,503	2.53
Restricted stock	64,380		2.34
Total	$	105,883

Summary of Changes in Number of Shares of Common Stock Under Option

The following summarizes the changes in the number of shares of common stock under option for the three months ended March 31, 2021 (shares/options and aggregate intrinsic value in thousands):

	Shares	Weighted Average Exercise Price		Options Exercisable at End of Period	Weighted Average Exercise Price of Exercisable Options		Weighted Average Fair Value of Options Granted  During the Period		Aggregate Intrinsic Value
Outstanding at December 31, 2020	4,964	$	146.69	3,994	$	130.37			$	626,107
Granted	164	264.85					$	73.15
Exercised	(283)	94.72							49,124
Forfeited	—	—
Outstanding at March 31, 2021	4,845	$	153.72	3,801	$	134.85			$	556,757
Expected to vest as of March 31, 2021	1,044	$	222.43

Schedule of Weighted-Average Assumptions

The fair value of stock option awards granted was estimated using the Black-Scholes option pricing model with the following weighted-average assumptions for grants or modifications during the three months ended March 31, 2021 and 2020:

	March 31,
	2021		2020
Risk-free interest rate	0.35	%	0.41	%
Dividend yield	—		—
Expected volatility	34.66	%	30.29	%
Expected life (in years)	4.0		3.8

Summary of Changes in Number of Shares of Restricted Stock and Restricted Stock Units

The following table summarizes the changes in the number of shares of restricted stock and restricted stock units for the three months ended March 31, 2021 (shares in thousands): 

	Shares	Weighted Average Grant Date Fair Value
Outstanding at December 31, 2020	174	$	265.29
Granted	200	272.68
Vested	(29)	267.88
Canceled or forfeited	(23)	288.54
Outstanding at March 31, 2021	322	$	268.02