Our Amended and Restated 1999 Stock Incentive Plan (the “Plan”) provides for grants of equity-based awards to employees, directors and officers, and advisors (“Eligible Persons”). The Plan is designed to promote the interests of the company using equity investment interests to attract, motivate, and retain individuals.

A maximum of 8,000,000 shares are authorized under the Plan. All awards have restriction periods tied primarily to employment and/or service. The Plan allows for accelerated or continued vesting in certain circumstances as defined in the Plan including death, disability, a change in control, and termination or retirement. The Board of Directors, or a committee appointed by the Board, has discretion subject to limits defined in the Plan, to modify the terms of any outstanding award. Awards granted to directors are made in exchange for their services to the company as directors and therefore, the guidance in FASB ASC Topic is not applicable.

Under the Plan, the Board, or a committee appointed by the Board, may impose restrictions on the exercise of awards during blackout periods. Insiders may participate in plans established pursuant to Rule under the Exchange Act that allow them to exercise awards subject to criteria.

We recognize stock-based compensation expense based on the estimated fair value of awards in accordance with FASB ASC Topic 718 . Stock-based compensation expense fluctuates over time as a result of the vesting periods for outstanding awards and the number of awards that actually vest. The following table reflects the components of stock-based compensation expense recognized in the Condensed Consolidated Statements of Operations for the three- and month periods ended June 30, 2021 and 2020:

Eligible employees may receive stock option awards annually with the number of shares and type of instrument generally determined by the employee’s salary grade and performance level. Incentive and stock option awards allow the recipient to purchase shares of our common stock at a set price, not to be less than the closing market price on the date of award, for no consideration payable by the recipient. The related number of shares underlying the stock option is fixed at the time of the grant. Options generally vest over a four-year period with a maximum term of five years from the vesting date. In addition, certain management and professional level employees may receive stock option awards upon the commencement of employment.

The fair value of each award is estimated as of the date of the grant using the Black-Scholes valuation model. The expected volatility reflects the consideration of the historical volatility of our common stock as determined by the closing price over a to term commensurate with the expected term of the award. Expected dividends reflect the amount of quarterly distributions authorized and declared on our Class A and Class B common stock as of the grant date. The expected term of the awards is based on evaluations of historical and expected future employee exercise behavior. The risk-free interest rates for periods within the expected term of the award are based on the U.S. Treasury yield curve in effect during the period the options were granted. We have used historical data to estimate future forfeiture rates to apply against the gross amount of compensation expense determined using the valuation model. These estimates have approximated our actual forfeiture rates.

The weighted-average assumptions used to estimate the fair value of the stock options using the Black-Scholes valuation model were as follows for the three- and periods ended June 30, 2021 and 2020:

Activity with respect to the company’s option awards during the period ended June 30, 2021 is as follows:

Activity with respect to the company’s restricted stock awards during the period ended June 30, 2021 is as follows:

As of June 30, 2021, there was $0.1 million of total unrecognized compensation cost related to stock option awards. This cost is expected to be recognized over a weighted-average period of 2.1 years.