On November 18, 2015, the Company’s Board of Directors adopted and approved the 2015 Equity Incentive Plan (the 2015 Plan), which authorized the Company to grant up to 223,424 ordinary shares in the form of incentive share options, nonstatutory share options, share appreciation rights, restricted share awards, restricted share units and other share awards. The types of share-based awards, including the rights amount, terms, and exercisability provisions of grants are determined by the Company’s Board of Directors. The purpose of the 2015 Plan is to provide the Company with the flexibility to issue share-based awards as part of an overall compensation package to attract and retain qualified personnel. On May 18, 2017, the Company amended the 2015 Plan to increase the number of ordinary shares available for issuance under the 2015 Plan by 219,605 shares to 443,029 shares.

On March 14, 2018, the Company’s Board of Directors adopted and approved the 2018 Equity Incentive Plan (the 2018 Plan), which became effective upon the execution and delivery of the underwriting agreement related to the Company’s IPO. No further grants will be made under the 2015 Plan. The ordinary shares underlying any options that are forfeited, cancelled, repurchased or are otherwise terminated by the Company under the 2015 Plan will not be added back to the ordinary shares available for issuance.

The 2018 Plan authorizes the Company to grant up to 1,018,459 ordinary shares in the form of incentive share options, nonstatutory share options, share appreciation rights, restricted share awards, restricted share units, performance share awards, performance cash awards and other share awards. The types of share-based awards, including the amount, terms, and exercisability provisions of grants are determined by the Company’s Board of Directors. The ordinary shares underlying any options that are forfeited, cancelled, repurchased or are otherwise terminated by the Company under the 2018 Plan will be added back to the ordinary shares available for issuance under the 2018 Plan.

On December 5, 2018, pursuant to powers delegated to it by the Board of Directors of the Company, the Compensation Committee approved an increase in the number of ordinary shares available to be granted pursuant to the 2018 Plan by 4% of the total number of shares of the Company’s issued share capital on December 31, 2018, being 574,081 ordinary shares.

On February 14, 2020, pursuant to powers delegated to it by the Board of Directors of the Company, the Compensation Committee approved, by written resolution, an increase of 594,758 ordinary shares to the number of ordinary shares available to be granted pursuant to the 2018 Plan, being just under 4% of the total number of the Company’s ordinary shares outstanding shares on December 31, 2019, in accordance with the terms of the 2018 Plan.

On June 10, 2020, at the Company’s annual general meeting of shareholders, the shareholders approved and adopted an amended and restated 2018 Plan which, among other things includes an increase of 2,250,000 ordinary shares in the number of ordinary shares reserved for issuance under the 2018 Plan. 

Restricted Ordinary Shares

In connection with the Company’s formation, 413,110 restricted ordinary shares were issued on October 14, 2015 to the Company’s founders at par value. These ordinary shares are subject to various restrictions pursuant to ordinary share purchase agreements between the Company and each founder, including restrictions on transfer and a Company right of repurchase. The restricted ordinary shares were 25% vested as of October 14, 2016 and 1/36^th of the remaining restricted ordinary shares vested on a monthly basis thereafter (subject to acceleration of vesting in connection with certain change of control transactions). A change in status occurred on November 18, 2015 when the founders became employees of the Company. The grant date of these shares is now considered to be November 18, 2015 when the fair value was $3.14 per share.

Restricted ordinary shares were fully vested as of December 31, 2019 and there was no restricted ordinary share activity for the year ended December 31, 2020.

The Company recorded share-based compensation expense for the restricted ordinary shares based on the grant date fair value. The Company recorded an expense of $260 and $332 for the years ended December 31, 2019 and 2018, respectively. There was no unamortized compensation expense related to restricted ordinary shares as of December 31, 2020 or December 31, 2019. Total unamortized compensation expense related to restricted ordinary shares was $260 as of December 31, 2018 and was recognized over a weighted average period of 0.79 years.

Share Options

Unless specified otherwise in an individual option agreement, share options granted under the 2015 Plan and the 2018 Plan generally have a ten year term and a four year vesting period. The vesting requirement is conditioned upon a grantee’s continued service with the Company during the vesting period. Once vested, all awards are exercisable from the date of grant until they expire. The option grants are non-transferable. Vested options generally remain exercisable for 90 days subsequent to the termination of the option holder’s service with the Company. In the event of an option holder’s disability or death while employed by or providing service to the Company, the exercisable period extends to twelve months or eighteen months, respectively.

The fair value of options granted during the years ended December 31, 2020, 2019 and 2018 was estimated using the Black-Scholes option-pricing model. The inputs for the Black-Scholes model require management’s significant assumptions. The risk-free interest rate was based on a normalized estimate of the 7-year U.S. treasury yield. The Company has estimated the expected term utilizing the “simplified” method for awards that qualify as “plain vanilla”. The Company does not have sufficient company-specific historical and implied volatility information and it therefore estimates its expected share volatility based on historical volatility information of reasonably comparable guideline public companies and itself. The Company expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded share price. Expected dividend yield is based on the fact that the Company has never paid cash dividends, its ability to pay cash dividends is currently prohibited by the terms of its credit facility with SVB and the Company’s future ability to pay cash dividends on its shares may be limited by the terms of any future debt or preferred securities. The Company has elected to account for forfeitures as they occur.

The Company granted 64,840, 512,778 and 479,986 share options to employees and directors during the years ended December 31, 2020, 2019 and 2018, respectively. There were 266,666, 837,386 and 479,986 unvested employee and director options outstanding as of December 31, 2020, December 31, 2019 and December 31, 2018, respectively. Total expense recognized related to the employee and director share options was $1,136, $1,388 and $669 for the years ended December 31, 2020, 2019 and 2018, respectively. Total unamortized compensation expense related to employee and director share options was $970, $3,342 and $2,822 as of December 31, 2020, December 31, 2019 and December 31, 2018, respectively, expected to be recognized over a remaining weighted average vesting period of 1.47 years, 2.61 years and 3.07 years as of December 31, 2020, December 31, 2019 and December 31, 2018, respectively.

The range of assumptions that the Company used to determine the grant date fair value of employee and director options granted were as follows:

The following table summarizes the number of options outstanding and the weighted-average exercise price:

The aggregate intrinsic value of share options is calculated as the difference between the exercise price of the share options and the fair value of the Company’s ordinary shares for those share options that had exercise prices lower than the fair value of the Company’s ordinary shares as of December 31, 2020 and December 31, 2019.

The weighted average grant-date fair value per share of share options granted during the years ended December 31, 2020, 2019 and 2018 was $1.28, $3.80 and $7.25, respectively.

Restricted Share Units (RSUs)

No RSUs were granted to directors during the year ended December 31, 2020. The Company granted 31,367 and 36,924 RSUs to directors during the years ended December 31, 2019 and 2018, respectively.  

The table below shows the number of RSUs granted covering an equal number of the Company’s ordinary shares and the weighted-average grant date fair value of the RSUs granted:

The fair value of the RSUs is determined on the date of grant based on the market price of the Company’s ordinary shares on that date. The fair value of RSUs is expensed ratably over the vesting period, which is generally one year for directors. Total expense recognized related to the RSUs was $63 and $313 for the years ended December 31, 2020 and 2019, respectively. There was no unamortized compensation expense related to the RSUs as of December 31, 2020. Total unamortized compensation expense related to the RSUs was $99 as of December 31, 2019, expected to be recognized over a remaining average vesting period of 0.45 years as of December 31, 2019.

The Company awarded 1,079,000 and 50,000 RSUs to certain employees during the years ended December 31, 2020 and 2019, respectively, which are subject to certain vesting conditions (Performance RSUs). No Performance RSUs were awarded prior to the year ended December 31, 2018.

The table below shows the number of Performance RSUs granted covering an equal number of the Company’s ordinary shares and the weighted-average grant date fair value of the Performance RSUs granted:

The weighted average grant date fair value of Performance RSUs with a market condition was determined using the Monte Carlo simulation model. The fair value of Performance RSUs is expensed ratably over the vesting period. Total expense recognized related to the Performance RSUs was $1,560 and $212 for the years ended December 31, 2020 and 2019, respectively. Total unamortized compensation expenses related to Performance RSUs was $152 and $198 for the years ended December 31, 2020 and 2019, respectively, expected to be recognized over a remaining average vesting period of 0.20 years and 0.81 years as of December 31, 2020 and 2019, respectively.

The Company’s share-based compensation expense was classified in the consolidated statements of operations and comprehensive loss as follows:

There was a total of $1,122, $3,639 and $3,273 unamortized share-based compensation expense for restricted ordinary shares, options, restricted share units and performance restricted share units as of December 31, 2020, December 31, 2019 and December 31, 2018, respectively, expected to be recognized over a remaining average vesting period of 0.80 years, 2.44 years and 2.71 years as of December 31, 2020, December 31, 2019 and December 31, 2018, respectively.