Under the Company’s current 2015 Stock Incentive Plan (the “2015 Plan”), the Company’s Board of Directors (the “Board of Directors”) has flexibility to determine the type and amount of awards to be granted to eligible participants, who must be employees, directors, officers or consultants of the Company or its subsidiaries. The 2015 Plan allows for grants of incentive stock options, nonqualified stock options, restricted stock awards, stock appreciation rights, and restricted units. The aggregate number of shares of common stock that may be granted through awards under the 2015 Plan to any employee in any calendar year may not exceed 500 shares. The 2015 Plan will continue in effect until December 2025 unless terminated sooner.  As of December 31, 2020, the number of shares authorized and reserved for issuance under the 2015 Plan is 6,800 shares, subject to automatic annual increase equal to 5% of the total number of shares of the Company’s outstanding common stock.

Options Granted:

During the year ended December 31, 2020, the Company issued stock options for an aggregate of 1,098 shares under the 2015 Plan to directors and employees of the Company. The options issued during the year ended December 31, 2020 generally vest and become exercisable over a period of one year to five years and expire ten years from the date of the grant.

For computing the fair value of the stock-based awards, the fair value of each option grant has been estimated as of the date of grant using the Black-Scholes option-pricing model with the following assumptions:

(a)Expected volatility is based upon the Company’s historical volatility.

(b)Because the Company does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term for these grants, the Company utilized the simplified method in developing an estimate of the expected term of these options.

Using these assumptions, the fair value of the stock options granted during the years ended December 31, 2020, 2019, and 2018 was $5,310, $952, and $6,059, respectively, which will be amortized as stock-based compensation expense over the vesting period of the options.

The total non-cash stock compensation expense related to stock options and restricted stock awards recorded by the Company was as follows:

For the years ended December 31, 2020, 2019, and 2018, the majority of stock-based compensation costs were classified as selling, general and administrative expense. A summary of changes in outstanding options and restricted stock awards during the year ended December 31, 2020 is as follows:

The following table summarizes the exercise price range, weighted average exercise price, and remaining contractual lives by significant ranges for options outstanding and exercisable as of December 31, 2020:

The intrinsic value of options exercised was $2,006, $607, and $315 during the years ended December 31, 2020, 2019, and 2018, respectively. The intrinsic value of restricted stock awards vested was $0, $3,252, and $2,720 during the years ended December 31, 2020, 2019, and 2018, respectively. Total fair value of options vested during the years ended December 31, 2020, 2019, and 2018 was $1,722, $1,610, and $1,757, respectively. Total fair value of restricted stock awards vested during the years ended December 31, 2020, 2019, and 2018 was $0, $919, and $1,076, respectively.

The fair value of unvested restricted stock awards is determined based on the market price of our shares of common stock on the grant date or using the Monte-Carlo pricing model. As of December 31, 2020, there were 1,814 unvested stock options and unrecognized compensation cost of $7,413 related to unvested stock options, as well as 600 unvested restricted stock awards and unrecognized compensation cost of $2,430 related to unvested restricted stock awards. Unrecognized compensation cost of unvested stock options and restricted stock awards are expected to be recognized over the weighted average period of 2.6 years and 2.3 years, respectively.