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Stockholders' Equity and Stock-Based Compensation
12 Months Ended
Dec. 31, 2023
Equity [Abstract]  
Stockholders' Equity and Stock-Based Compensation Stockholders' Equity and Stock-Based Compensation
Preferred Stock
We have authorized 5.0 million shares of preferred stock, par value $0.0001, none of which is issued and outstanding.

Common Stock
Each share of common stock has the right to one vote. The holders of common stock are also entitled to receive dividends whenever funds are legally available and when declared by the Board of Directors, subject to the prior rights of holders of all classes of stock outstanding having priority rights as to dividends. No dividends have been declared or paid as of December 31, 2023.

Public Offering
In March 2021, we closed a follow-on public offering in which we issued and sold approximately 2.5 million shares of common stock (including approximately 0.3 million shares sold pursuant to the full exercise of the underwriters'
option to purchase additional shares) at an offering price of $34.00 per share, resulting in aggregate net proceeds to us of approximately $82.4 million after deducting underwriting discounts, commissions and offering costs.

Common Stock Repurchase Plan
On November 14, 2019, our Board of Directors authorized the repurchase of up to $10.0 million of our outstanding shares of common stock. As of December 31, 2023, no repurchases had been executed under the program.

Equity Incentive Plan
As of December 31, 2023, there were approximately 1.7 million shares available for issuance under our equity incentive plan. Common stock issued for awards will come from newly issued shares.

Restricted Stock Awards and Units
Restricted stock award (RSA) and restricted stock unit (RSU) activity under our equity incentive plan was as follows (in thousands, except weighted-average grant date fair values):
Number of Restricted Stock AwardsWeighted-Average Grant Date Fair Value
RSAs at December 31, 2022332 $28.24 
Awards granted(32)33.66 
Awards vested(167)25.46 
RSAs at December 31, 2023133 30.44 

Number of Restricted Stock UnitsWeighted-Average Grant Date Fair Value
RSUs at December 31, 20222,784 $17.63 
Awards granted1,639 10.79 
Awards vested(1,268)17.96 
Awards forfeited(338)19.52 
RSUs at December 31, 20232,817 13.27 

The total fair value of RSAs and RSUs vested during the year ended December 31, 2023 was $4.3 million and $22.8 million, respectively. Awards outstanding as of December 31, 2023 include 0.8 million performance-based awards that will vest upon meeting certain performance criteria. Approximately 0.5 million total performance-based awards were granted in 2023. The awards vest based on a market metric called Total Shareholder Return ("TSR") for the performance period of three years relative to the TSR of companies in the Russell 2000 Index had a weighted average grant-date fair value of $14.21 per share using a Monte Carlo simulation pricing model.

Stock Options
The following table summarizes our stock option activity during the year ended December 31, 2023 (in thousands, except weighted-average exercise prices):
 Number of OptionsWeighted-Average Exercise PriceWeighted-Average Remaining Contractual Term (Years)Aggregate Intrinsic Value
Outstanding, December 31, 20221,827 $1.293.4$16,156
Options exercised(428)$1.50
Options canceled(1)$1.26
Outstanding, December 31, 20231,398 $1.242.5$17,142
Options exercisable at December 31, 20231,398 $1.242.5$17,142
Options vested as of December 31, 2023, and expected to vest after December 31, 20231,398 $1.242.5$17,142
Total intrinsic value of options exercised for the years ended December 31, 2023, 2022 and 2021 was $4.2 million, $7.7 million and $27.1 million, respectively. We received proceeds of $0.6 million, $1.2 million and $1.1 million from the exercise of options for each of the years ended December 31, 2023, 2022 and 2021, respectively.

Employee Stock Purchase Plan
Information related to activity under our Employee Stock Purchase Plan (ESPP) was as follows:
 Year Ended
December 31, 2023
Shares issued (in thousands)263 
Weighted-average per share purchase price$9.40 
Weighted-average per share discount from the fair value of our common stock on date of issuance$1.66 

As of December 31, 2023, there were 4.1 million shares available for grant under the ESPP.

Stock-Based Compensation
Total stock-based compensation expense was included in our Consolidated Statements of Operations as follows (in thousands):
Year Ended December 31,
202320222021
Cost of revenues$2,406 $2,677 $2,505 
Research and development9,866 11,675 13,433 
Sales, general and administrative13,560 12,405 21,782 
$25,832 $26,757 $37,720 

Unrecognized Compensation Costs
As of December 31, 2023, total unrecognized stock-based compensation was $30.9 million, which will be recognized over an average expected recognition period of 1.8 years.