In 2015, the Company adopted (i) the Amended and Restated 2015 Stock Option and Grant Plan and (ii) the 2015 Stock Incentive Plan (together the “2015 Stock Option Plans”) under which it may grant incentive stock options (“ISOs”), nonqualified stock options (“NSOs”) for the right to purchase shares of common stock and grant restricted stock units (“RSUs”). The 2015 Stock Option Plans reserve 5.0 million shares of common stock for issuance as ISOs, 0.5 million shares of RSUs and 0.25 million shares for issuance under the 2015 Stock Incentive Plan. Under the 2015 Stock Option Plans, ISOs may not be granted at less than fair market value on the date of the grant and generally vest over a four-year period based on continued service. Options generally expire ten years after the grant date.

As of March 31, 2020, 0.6 million shares were available for issuance under the 2015 Stock Option Plans, including less than 0.1 million shares available for issuance under the 2015 Stock Incentive Plan. The Company currently uses authorized and unissued shares to satisfy share award exercises.

In November 2017, the Company’s Board of Directors adopted the 2017 Long Term Incentive Plan (the “2017 Plan”) under which it may grant stock options, NSOs to purchase shares of common stock and RSUs. As of March 31, 2020, the Company had reserved 17.7 million shares of common stock available for issuance under the 2017 Plan to employees, directors, officers and consultants of the Company and its subsidiaries. The number of shares of common stock available for issuance under the 2017 Plan is increased on each January 1 by 4.4 million shares of common stock. Options and RSUs granted to employees under the 2017 Plan generally vest over four years. Common stock subject to an award that expires or is canceled, forfeited, exchanged or otherwise terminated without delivery of shares, and shares withheld or surrendered to pay the exercise price of, or to satisfy the withholding obligations with respect to an award, will become available for future grants under the 2017 Plan. At March 31, 2020, 11.8 million shares were available for issuance under the 2017 Plan. The Company currently uses authorized and unissued shares to satisfy share award exercises.

The fair value for the Company’s stock options granted and Employee Stock Purchase Plan (the "ESPP") purchase rights, as discussed further below, during the periods presented were estimated at grant date using a Black Scholes option-pricing model using the following weighted average assumptions:

	Stock Options				ESPP
	March 31, 2020		March 31, 2019		March 31, 2020		March 31, 2019
Expected dividend rate	0%		0%		0%		0%
Expected volatility	56.2%		39.8%		48.1%		46.0%
Risk-free interest rate	1.53%		2.48% - 2.59%		1.57%		2.44%
Expected term (in years)		6.25		6.25		0.50		0.42

The following table summarizes stock option activity for the three months ended March 31, 2020:

	Number of Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
	(In thousands)			(Per share)		(Years)		(In thousands)
Balances at December 31, 2019		2,786		$	13.67		7.7	$	31,489
Granted		524		$	25.42
Exercised		(228	)	$	5.77
Forfeited		(136	)	$	19.04
Balances at March 31, 2020		2,946		$	16.13		7.8	$	12,663
Options vested and expected to vest at March 31, 2020		2,946		$	16.13		7.8	$	12,663
Options vested and exercisable at March 31, 2020		1,210		$	9.27		6.3	$	9,703

The Company expects all outstanding stock options to fully vest. The weighted average grant date fair value per share for the three months ended March 31, 2020 and 2019 was $13.74 and $12.92, respectively. The total fair value of shares vested for the three months ended March 31, 2020 and 2019 was $3.0 million and $2.4 million, respectively.

The total unrecognized compensation expense related to non-vested stock options granted is $16.5 million and is expected to be recognized over a weighted average period of 2.8 years as of March 31, 2020.

In 2014 and 2015, the Company granted shares of the Company’s common stock (the “incentive units”) to certain members of management pursuant to restricted stock agreements (the “RSAs”).

The incentive units were granted with an exercise price equal to the fair market value on the date of grant, are subject to vesting, and if exercised in advance of vesting were subject to the Company’s right to repurchase until vested.

The Company did not grant any additional incentive units during the three months ended March 31, 2020 or 2019. During the first quarter of 2019, all of the remaining 0.7 million incentive units were vested with a weighted average grant date fair value of $0.05 per share. Therefore, subsequent to the first quarter of 2019, we incurred no additional stock-based compensation expense and there is no further unrecognized compensation expense or intrinsic value related to non-vested incentive units.

The following table summarizes the RSU activity for the Company for the three months ended March 31, 2020:

	Number of Shares			Weighted Average Grant Date Fair Value		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
	(In thousands)			(Per share)		(Years)		(In thousands)
Balances at December 31, 2019		1,881		$	23.08		1.6	$	44,386
Granted		1,219		$	25.39
Vested		(271	)	$	26.41
Forfeited		(111	)	$	22.98
Balances at March 31, 2020		2,718		$	23.79		1.8	$	41,361
Units expected to vest at March 31, 2020		2,718		$	23.79		1.8	$	41,361

The Company expects all outstanding RSUs to fully vest. The total unrecognized compensation related to RSUs was $59.5 million as of March 31, 2020 and is expected to be recognized over a weighted average period of 3.2 years.

The Company initially reserved 1.8 million shares of common stock for issuance under the ESPP. The number of shares available for issuance under the ESPP increases each January 1 by 0.9 million shares of common stock. The ESPP will continue in effect unless terminated prior thereto by the Company’s board of directors or compensation committee, each of which has the right to terminate the ESPP at any time. As of March 31, 2020, 3.0 million shares were available for issuance under the ESPP Plan.

During the three months ended March 31, 2020, there was no ESPP activity as the current offering period is December 3, 2019 through June 3, 2020. During the three months ended March 31, 2019, there was no ESPP activity as the offering period was January 2, 2019 to June 3, 2019.

A summary of the Company’s stock-based compensation expense, which includes stock options, incentive units, RSUs and ESPP, is presented below:

	Three Months Ended
	March 31, 2020		March 31, 2019
	(In thousands)
Stock options	$	1,391	$	1,244
Incentive units		—		351
RSUs		4,198		2,328
ESPP		602		716
Total stock-based compensation expense	$	6,191	$	4,639

A summary of the Company’s stock-based compensation expense as recognized on the condensed consolidated statements of operations is as follows:

	Three Months Ended
	March 31, 2020		March 31, 2019
	(In thousands)
Cost of revenue - subscription	$	389	$	260
Cost of revenue - services and other		427		349
Research and development		1,501		917
General and administrative		1,002		1,371
Sales and marketing		2,872		1,742
Total stock-based compensation expense	$	6,191	$	4,639