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Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2020

Information Regarding Stock Options Outstanding Stock Options Vested and Expected to Vest and Stock Options Exercisable

Information regarding the Company’s stock options outstanding, stock options vested and expected to vest, and stock options exercisable at December 31, 2020, was as follows (in thousands except weighted average exercise price and contractual term):

	Number of Shares		Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value
Balances at December 31, 2020
Stock options outstanding		16,306	$	4.71		5.26	$	36,180
Stock options vested and expected to vest		16,151		4.70		5.22		35,905
Stock options exercisable		12,735		4.61		4.36		29,535

Recognition of Stock-Based Compensation Expense

Stock-based compensation expense recognized on the Company’s consolidated statements of operations for the years ended December 31, 2020, 2019 and 2018, was as follows (in thousands):

	Year Ended December 31,
	2020		2019		2018
Research and development	$	3,739	$	2,472	$	1,669
Selling, general and administrative		14,290		10,840		8,725
Total stock-based compensation expense	$	18,029	$	13,312	$	10,394

Weighted Average Assumptions Used to Value Stock-Based Awards

The weighted average assumptions used to value the Company’s stock-based awards for the years ended December 31, 2020, 2019 and 2018, was as follows:

	Year Ended December 31,
	2020		2019		2018
Stock Options:
Expected term (in years)		6.89		5.59		6.07
Estimated volatility	52%		50%		50%
Risk-free interest rate	0.94%		2.32%		2.72%
Expected dividend yield	0%		0%		0%
Employee Stock Purchase Plan Rights:
Expected term (in years)		0.72		0.80		0.74
Estimated volatility	53%		46%		47%
Risk-free interest rate	0.86%		2.04%		2.34%
Expected dividend yield	0%		0%		0%

2008 Equity Incentive Plan

Activity Under Equity Incentive Plans Related to Stock Options

Activity under the Company’s equity incentive plans related to stock options is set forth below (in thousands except per share amounts):

	Number of Options Outstanding			Weighted Average Exercise Price per Share
Balances at December 31, 2019		16,830		$	4.53
Granted		2,237			5.22
Exercised		(2,658	)		4.01
Forfeited/canceled		(103	)		5.27
Balances at December 31, 2020		16,306			4.71

Activity Under Equity Incentive Plans Related to RSUs

Activity under the Company’s equity incentive plans related to RSUs is set forth below (in thousands except per share amounts):

	Number of RSUs Unvested			Weighted Average Grant Date Fair Value per Share
Balances at December 31, 2019		4,098		$	5.24
Granted ⁽¹⁾		3,433			5.17
Vested ⁽¹⁾		(1,631	)		5.05
Forfeited⁽¹⁾		(161	)		5.73
Balances at December 31, 2020		5,739			5.24

(1)

Includes shares issuable under performance-based restricted stock unit awards.