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Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2021

Share-based Payment Arrangement [Abstract]

The Company recognized share-based compensation expense by function as follows, in thousands:


	Years Ended December 31,
	2021		2020		2019
Selling, general and administrative	$	36,884	$	33,919	$	25,686
Research and development	33,489		26,001		27,361
Total share-based compensation expense	$	70,373	$	59,920	$	53,047

Share-based Payment Arrangement, Cost by Plan

The Company recognized share-based compensation expense by grant type as follows, in thousands:


	Years Ended December 31,
	2021		2020		2019
Stock options	$	46,946	$	54,710	$	36,393
Performance-based restricted stock units	12,752		1,804		15,351
Restricted stock units	9,664		2,716		1,213
Employee stock purchase plan	1,011		690		90
Total share-based compensation expense	$	70,373	$	59,920	$	53,047

Weighted-Average Assumptions and Estimated Fair Value of Stock Options

The fair value of each option issued to employees was estimated on the date of grant using the Black-Scholes option pricing model with the following weighted-average assumptions:


	Years Ended December 31,
	2021		2020		2019
Expected volatility	53	%	57	%	64	%
Expected term (in years)	4.27		4.51		4.47
Risk-free interest rate	0.6	%	0.7	%	2.3	%
Expected dividend yield	0.0	%	0.0	%	0.0	%

Summary of Stock Option Activity

The following table summarizes the stock option activity under the Company’s stock option plans during the year ended December 31, 2021 (in thousands, except per share amounts and years):


	Options	Weighted- Average Exercise Price		Weighted- Average Contractual Life (in years)	Intrinsic Value(1)
Outstanding at January 1, 2021	8,699	$	40.33
Granted	1,808	73.27
Exercised	(1,402)	32.44
Forfeited/cancelled/expired	(1,104)	53.72
Outstanding at December 31, 2021	8,001	$	47.31	4.27	$	365,079
Exercisable at December 31, 2021	4,576	$	38.10	3.34	$	250,968

______________________

(1)The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying options and the estimated fair value of the common stock for the options that were in the money at December 31, 2021.

Summary of Restricted Stock Awards, Restricted Stock Unit Awards and Performance Awards Activity

The following table summarizes the Company’s RSU activity during the year ended December 31, 2021, in thousands (except grant date fair value data):


	Number of Shares	Weighted- Average Grant Date Fair Value
Non-vested at December 31, 2020	243	$	54.00
Granted	696	72.66
Released	(77)	53.43
Forfeited/cancelled	(144)	68.29
Non-vested at December 31, 2021	718	$	69.29

The following table summarizes the Company’s PRSU activity during the year ended December 31, 2021, in thousands (except grant date fair value data):


	Number of Shares	Weighted- Average Grant Date Fair Value
Non-vested at January 1, 2021	273	$	27.97
Granted(1)	434	50.82
Released	(273)	27.97
Forfeited/cancelled	(67)	52.77
Non-vested at December 31, 2021	367	$	50.46

_____________________

(1)Pursuant to the terms of the awards granted, the actual number of awards earned could range between 0% and 200% of the above number of awards granted. The amount disclosed represents PRSU grants at maximum payout.