Stock-Based Compensation	6 Months Ended
Jun. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	8. Stock-Based Compensation For stock-based awards granted by the Company, stock-based compensation expense is measured at grant date based on the fair value of the award and is expensed over the requisite service period. The Company recorded stock-based compensation expense of $567 and $762 for the three months ended June 30, 2020 and 2019, respectively, and $1,013 and $1,447 for the six months ended June 30, 2020 and 2019, respectively. Stock Options The Company uses the Black-Scholes option-pricing model to estimate the fair value of options. This model requires the input of highly subjective assumptions including the expected volatility, risk-free interest rate and the expected life of options. There were no stock options granted during the three and six months ended June 30, 2020. The Company estimates the expected volatility of its common stock and expected life of its stock options based on its own historical experience. The expected volatility reflects the actual historical volatility of the price of the Company’s common stock since it began trading publicly in March 2013. The expected life represents the period of time that stock options are expected to be outstanding, based on historical exercise and employee departure behavior. The Company has no history or expectation of paying cash dividends on its common stock. The risk-free interest rate is based on the U.S. Treasury yield for a term consistent with the expected life of the options in effect at the time of grant. There were no exercises of stock options during the three and six months ended June 30, 2020 and 2019. Compensation expense, net of estimated forfeitures, is recognized ratably over the requisite service period. As of June 30, 2020, there was $117 of unrecognized compensation expense related to stock options, which is expected to be recognized over a weighted-average period of 1.8 years. RSUs As of June 30, 2020, there was $2,584 of unrecognized compensation expense, net of estimated forfeitures, related to RSUs, which is expected to be recognized over a weighted-average period of 2.2 years. The Company uses the fair market value of the underlying common stock on the dates of grant to determine the fair value of RSUs. Employee Stock Purchase Plan The Company estimates the fair value of purchase rights under the 2013 ESPP using the Black-Scholes valuation model. The fair value of each purchase right under the 2013 ESPP is estimated on the date of grant using the Black-Scholes option valuation model and the straight-line attribution approach with assumptions substantially similar to those used for the valuation of stock option awards, with the exception of the expected life. The expected life is estimated to be six months, which is consistent with the purchase periods under the 2013 ESPP.

Stock-Based Compensation

6 Months Ended

Jun. 30, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

8. Stock-Based Compensation

For stock-based awards granted by the Company, stock-based compensation expense is measured at grant date based on the fair value of the award and is expensed over the requisite service period. The Company recorded stock-based compensation expense of $567 and $762 for the three months ended June 30, 2020 and 2019, respectively, and $1,013 and $1,447 for the six months ended June 30, 2020 and 2019, respectively.

Stock Options

The Company uses the Black-Scholes option-pricing model to estimate the fair value of options. This model requires the input of highly subjective assumptions including the expected volatility, risk-free interest rate and the expected life of options. There were no stock options granted during the three and six months ended June 30, 2020.

The Company estimates the expected volatility of its common stock and expected life of its stock options based on its own historical experience. The expected volatility reflects the actual historical volatility of the price of the Company’s common stock since it began trading publicly in March 2013. The expected life represents the period of time that stock options are expected to be outstanding, based on historical exercise and employee departure behavior. The Company has no history or expectation of paying cash dividends on its common stock. The risk-free interest rate is based on the U.S. Treasury yield for a term consistent with the expected life of the options in effect at the time of grant.

There were no exercises of stock options during the three and six months ended June 30, 2020 and 2019.

Compensation expense, net of estimated forfeitures, is recognized ratably over the requisite service period. As of June 30, 2020, there was $117 of unrecognized compensation expense related to stock options, which is expected to be recognized over a weighted-average period of 1.8 years.

RSUs

As of June 30, 2020, there was $2,584 of unrecognized compensation expense, net of estimated forfeitures, related to RSUs, which is expected to be recognized over a weighted-average period of 2.2 years. The Company uses the fair market value of the underlying common stock on the dates of grant to determine the fair value of RSUs.

Employee Stock Purchase Plan

The Company estimates the fair value of purchase rights under the 2013 ESPP using the Black-Scholes valuation model. The fair value of each purchase right under the 2013 ESPP is estimated on the date of grant using the Black-Scholes option valuation model and the straight-line attribution approach with assumptions substantially similar to those used for the valuation of stock option awards, with the exception of the expected life. The expected life is estimated to be six months, which is consistent with the purchase periods under the 2013 ESPP.