Stock-Based Compensation

9 Months Ended

Sep. 30, 2021

Share-based Payment Arrangement [Abstract]

Stock-Based Compensation

Stock-Based Compensation

The Company allocates stock-based compensation expense related to equity plans for employees and non-employee directors among the cost of sales, research and development and other engineering expense, selling expense, or general and administrative expense based on the job functions performed by the employees or non-employee directors to whom the stock-based compensation is awarded. The Company recognized stock-based compensation expense related to its equity plans for employees of $2.6 million and $4.0 million for the three months ended September 30, 2021 and 2020, respectively, and $12.4 million and $9.5 million for the nine months ended September 30, 2021 and 2020, respectively.

During the nine months ended September 30, 2021, the Company granted 133,717 restricted stock units ("RSUs") to the Company's employees, including officers at an estimated weighted average fair value of $100.93 per share based on the closing price (adjusted for the present value of dividends) of the Company's common stock on the grant date. The RSUs granted to the Company's employees may be performance-based and/or time-based. Certain performance-based RSUs are granted to officers and key employees, where the number of performance-based awards to be issued is based on the achievement of certain Company performance criteria established in the RSU agreement over a cumulative three-year period. These awards cliff vest after three years. In addition, these same officers and key employees also receive time-based RSUs, which vest pursuant to a three-year graded vesting schedule. Time-based RSUs that are granted to the Company's employees excluding officers and certain key employees, vest ratably over the four year vesting-term of the award.

The Company’s seven non-employee directors are entitled to receive approximately $690 thousand in equity compensation annually. The number of shares ultimately granted are based on the average closing share price for the Company over the 60 day period prior to approval of the award in the second quarter of each year. In May and June 2021, the Company granted 6,601 shares of the Company's common stock to the non-employee directors, based on the average closing price of $114.60 per share and recognized a total expense of $756 thousand.

As of September 30, 2021, the Company's aggregate unamortized stock compensation expense was approximately $20.3 million, which is expected to be recognized in expense over a weighted-average period of 2.3 years.