NOTE 9. STOCK PLANS

Stock-Based Compensation

During the six months ended June 30, 2020, the Company granted options to purchase an aggregate of 551,500 shares of its common stock that are subject to time-based vesting conditions. 

The Company valued these stock options using the Black-Scholes Merton option pricing model. The following assumptions were used to compute the grant date fair values of the stock options granted during the six months ended June 30, 2020:

The assumptions used in calculating the fair values of purchase rights granted under the ESPP during the six months ended June 30, 2020 are set forth in the table below:

The Company’s stock-based compensation expense recognized for the periods presented was as follows:

Equity Award Activity

Restricted Stock Awards

The Company’s restricted stock award activity for the six months ended June 30, 2020 was as follows:

At June 30, 2020, total unrecognized compensation cost related to restricted stock was $57, which is expected to be recognized over a weighted average period of 0.3 year.

Restricted Stock Units

The Company’s restricted stock unit activity for the six months ended June 30, 2020 was as follows:

At June 30, 2020, total unrecognized compensation cost related to restricted stock units was $7,574, which is expected to be recognized over a weighted average period of 0.9 year.

Performance-Based Stock Options

The activity during the six months ended June 30, 2020 related to stock options that are subject to performance-based vesting conditions tied to the future achievement of stock price goals by the Company was as follows:

The weighted average grant date fair values of the performance-based stock options granted during the six months ended June 30, 2019 was $2.57 per share. No performance-based stock options were granted during the six months ended June 30, 2020 and no performance-based stock options vested during the six months ended June 30, 2020 and 2019. At June 30, 2020, total unrecognized compensation expense related to performance-based stock options was $17,259 and is expected to be recognized over a weighted average period of 2.9 years.

Stock Options

The activity during the six months ended June 30, 2020 related to all other stock options was as follows:

The weighted average grant date fair value of stock options granted during the six months ended June 30, 2020 and 2019 was $2.06 and $3.72 per share, respectively. The aggregate intrinsic value of the options exercised during the six months ended June 30, 2020 and 2019 was $177 and $177, respectively. The total grant date fair value of stock options vested during the six months ended June 30, 2020 and 2019 was $4,067 and $5,465, respectively. At June 30, 2020, total unrecognized compensation expense related to stock options was $5,122 and is expected to be recognized over a weighted average period of 2.4 years.

The aggregate intrinsic values in the tables above represent the difference between the fair market value of the Company’s common stock and the average option exercise price of in-the-money options, multiplied by the number of such options.

Employee Stock Purchase Plan

During the six months ended June 30, 2020, a total of 62,469 shares of common stock were purchased under the Company’s ESPP. As of June 30, 2020, accrued employee contributions for future purchases under the ESPP totaled $99.