In March 2011, our board of directors approved the 2011 Plan. The 2011 Plan provides for the grant of incentive and non-statutory stock options, stock appreciation rights, restricted shares of our common stock, stock units, and performance cash awards. We have shifted our stock-based compensation from stock options to RSUs and no stock options have been granted since 2014. As of December 31, 2020, 13,739,820 shares of common stock were reserved for issuance. As of December 31, 2020, options to purchase approximately 109,000 shares of common stock and RSUs covering approximately 951,000 shares of common stock were outstanding under the 2011 Plan.

No further awards will be made under our Amended and Restated 2001 Stock Incentive Plan, and it will be terminated. Options outstanding under the 2001 Plan will continue to be governed by their existing terms. As of December 31, 2020, no options to purchase shares of common stock were outstanding under the 2001 Plan.

Stock-based compensation expense for the years ended December 31, 2020, 2019 and 2018 amounted to $7,606, $8,596, and $12,268, respectively. For the year ended December 31, 2020, we recorded certain out-of-period adjustments that decreased stock-based compensation expense and net loss attributable to common stockholders by $481. The impact of these out-of-period adjustments is not considered material, individually, and in the aggregate, to any of the current or prior periods.

For the year ended December 31, 2020, we realized an income tax expense from stock-based compensation of $659. For the years ended December 31, 2019 and 2018, we realized an income tax benefit from stock-based compensation of $5,915 and $4,594, respectively. For the years ended December 31, 2020, 2019, and 2018, we capitalized $645, $860, and $789, respectively, of stock-based compensation expense.

We previously granted stock option awards to both employees and non-employee directors. A summary of the activity for stock option awards for 2020 is presented below:

The aggregate intrinsic value in the table above represents the difference between the estimated fair value of our common stock at December 31, 2020 and the option exercise price, multiplied by the number of in-the-money options at December 31, 2020. The intrinsic value changes are based on the estimated fair value of our common stock.

Stock options to purchase approximately 105,000, 69,000 and 972,000 shares of our common stock were exercised during the years ended December 31, 2020, 2019 and 2018 for cash proceeds of $708, $470 and $9,979, respectively. The total intrinsic value of stock options exercised for the years ended December 31, 2020, 2019 and 2018 was $697, $423 and $14,935, respectively.

We grant service-based restricted stock units (“RSUs”) to executive and non-executive personnel and non-employee directors. The service based RSUs granted to executive and non-executive personnel generally vest over a three-year period subject to continuous service on each vesting date. The service based RSUs for our non-employee directors generally vest over a one-year period for existing members and 33.3% per year over a three-year period for new members subject to continuous service on each vesting date.

We grant performance based RSUs to executive personnel. These awards vest subject to certain performance objectives based on revenue, Adjusted EBITDA, and/or relative total stockholder return performance goals achieved during the specified performance period and certain long-term service conditions. The maximum number of RSUs that may vest is determined based on actual Company achievement and performance based RSUs generally vest over a three-year period subject to continuous service on each vesting date and achievement of the performance conditions. We recognize stock-based compensation expense for performance based RSUs when performance targets are defined, and the grant date is established, and we believe that it is probable that the performance objectives will be met.

(1)

The performance-based RSUs granted to our executive officers in 2018 were subject to satisfaction of specified service based and performance based conditions. The performance objectives were subject to under- or over- achievement on a sliding scale, with a threshold of 50% of the target number of RSUs

and a maximum of 150% of the target RSUs. In March 2020, our Compensation Committee determined actual achievement of the 2018 performance-based RSUs at 100.5% resulting in the grant of additional RSUs in 2020 for the achievement above target.

(2)

The performance based RSUs granted to our executive officers in 2019 and 2020 were subject to the satisfaction of specified service based and performance based conditions over a three-year performance period. Achievement of the revenue and Adjusted EBITDA goals for the 2019 and 2020 performance based RSUs is based upon the budgets established for each of the years in the three-year performance period. In March 2020, our Compensation Committee determined actual achievement of the 2019 revenue and EBITDA goals for the 2019 performance based RSUs at 95% and 97%, respectively, resulting in the cancellation of RSUs in 2020 for the achievement below target. As the Company approves budgets on an annual basis, the performance targets for the 2019 performance based RSUs related to the 2020 and 2021 revenue and Adjusted EBITDA goals and the performance targets for the 2020 performance based RSUs related to the 2021 and 2022 revenue and Adjusted EBITDA goals were not considered defined as of the date these awards were awarded by the Compensation Committee. The grant date requirements of ASC 718, Compensation-Stock Compensation, are therefore not met until such approval is obtained. During the year ended December 31, 2020, the Company’s Compensation Committee approved the 2020 revenue and Adjusted EBITDA performance targets for the 2019 performance based RSUs resulting in additional RSUs granted of approximately 36,000 at a grant-date fair value of $12.41 per share. As of December 30, 2020, approximately 32,000 2019 performance based RSUs and approximately 151,000 2020 performance based RSUs have been excluded from RSU shares granted and non-vested as the performance targets have not yet been defined.

During the year ended December 31, 2020, approximately 453,000 shares of RSUs vested. The Company issued approximately 302,000 shares and the remaining shares were withheld to pay minimum statutory federal, state, and local employment payroll taxes on those vested awards.

At December 31, 2020, the total remaining stock-based compensation expense for unvested RSU awards is $9,907, which is expected to be recognized over a weighted average period of 1.7 years.