As of March 31, 2020, the Company’s stock incentive plans included the 2010 Stock Plan (the “2010 Plan”) and the 2020 Stock Plan (the “2020 Plan”) (together, the “Plans”), The 2020 Plan provides for the award of incentive stock options, non-qualified stock options, stock appreciation rights, restricted stock awards, restricted stock units, and other stock-based awards.

The 2010 Plan provided for the granting of incentive stock options and non-qualified stock options. As of the effective date of the 2020 Plan, no shares remained available for future issuance under the 2010 Plan and no further awards will be made under the 2010 Plan. Any options or awards outstanding under the 2010 Plan remain outstanding and effective. Shares of common stock subject to outstanding awards granted under the 2010 Plan that expire, terminate, or are otherwise surrendered, cancelled, forfeited, or repurchased by the Company are available for issuance under the 2020 Plan.

Stock options must be granted at an exercise price not less than 100% of the fair market value per share at the grant date. The maximum contractual term of options granted under the Plans is typically 10 years, options generally vest over four years with 25% of the shares underlying the option vesting at the end of the first year and the remaining vesting monthly over the following three years.

During the three months ended March 31, 2020 and 2019, 57,581 and 44,160 stock options were exercised under the Plans with total cash received upon option exercise of $177 and $115, respectively.

The fair value of each option award is determined on the date of grant using the Black Scholes Merton option-pricing model. The calculation of fair value includes several assumptions that require management’s judgment. The expected terms of options granted to employees during 2020 and 2019 were calculated using an average of historical exercises. Estimated volatility for the three months ended March 31, 2020 and 2019 incorporates a calculated volatility derived from the historical closing prices of shares of common stock of similar entities whose share prices were publicly available for the expected term of the option. The risk-free interest rate is based on the U.S. Treasury constant maturities in effect at the time of grant for the expected term of the option. The Company accounts for forfeitures as they occur, as such, the Company does not estimate forfeitures at the time of grant.

Prior to the Company’s IPO, where there was no public market for the Company’s common stock, the board of directors estimated the price of the Company’s common stock based upon several factors, including, but not limited to, third party valuations and the Company’s operating and financial performance. The third party valuations took into consideration several factors, including prices for preferred stock that were sold to outside investors in arm’s length transactions, and the rights, preferences, and privileges of the preferred stock and the common stock; the fact that the option grants involved illiquid securities in a private company; the Company’s stage of development and revenue growth; the state of the industry and the economy; the marketplace and major competitors; and the likelihood of achieving a liquidity event for the shares of common stock underlying the options, such as an initial public offering or sale of the Company, given prevailing market conditions. These valuations were performed in accordance with the American Institute of Certified Public Accountants’ Audit and Accounting Practice Aid, Valuation of Privately Held Company Equity Securities Issued as Compensation.

Subsequent to the Company’s IPO, the board of directors determined the exercise price of the Company’s stock options based on the closing price of the common stock as reported on the Nasdaq Global Select Market on the day of grant.

As of March 31, 2020, there were 2,204,251 shares available for grant under the 2020 Plan. As of December 31, 2019, there were 1,764,221 shares available for grant under the 2010 Plan. Following are the weighted average valuation assumptions used for options:

	Three Months Ended March 31,
	2020			2019
Valuation assumptions
Expected dividend yield		—	%		—	%
Expected volatility		60	%		57	%
Expected term (years)		4.49			6.05
Risk-free interest rate		1.44	%		2.54	%

The following table presents classification of stock-based compensation expense within the condensed consolidated statements of operations:

	Three Months Ended March 31,
	2020		2019
Cost of sales	$	253	$	89
Research and development		508		111
Sales and marketing		93		71
General and administrative		921		249
Total stock-based compensation	$	1,775	$	520

The weighted average grant date fair value of options granted during the three months ended March 31, 2020 and 2019 was $7.66 and $2.48, respectively. The intrinsic value of options exercised during the three months ended March 31, 2020 and 2019 was $1,231 and $77, respectively.

As of March 31, 2020, there was $32,031 of unrecognized compensation cost related to unvested stock options granted under the Plans, which is expected to be recognized over a weighted average period of 3.62 years. The fair value of shares vested during the three months ended March 31, 2020 and 2019 was $1,213 and $571, respectively.