We maintain three share-based employee compensation plans: the 2017 Equity Incentive Plan (“2017 Plan”), the 2014 Equity Incentive Plan (“2014 Plan”), and the 2012 Equity Incentive Plan (“2012 Plan”, and collectively with the 2017 Plan and the 2014 Plan, the “Stock Plans”). In January 2017, our board of directors adopted the 2017 Plan, and in February 2017 our stockholders approved the 2017 Plan, effective on March 1, 2017, which serves as the successor to the 2014 Plan and 2012 Plan and provides for the grant of incentive stock options to employees, including employees of any parent or subsidiary, and for the grant of nonstatutory stock options, stock appreciation rights, RSAs, RSUs, performance stock awards, performance cash awards, and other forms of stock awards to employees, directors, and consultants, including employees and consultants of our affiliates.

The following table summarizes the RSU activity during the six months ended June 30, 2019:

	Class A Outstanding RSUs			Class B Outstanding RSUs			Weighted- Average Grant Date Fair Value per RSU
	(in thousands, except per share data)
Unvested at December 31, 2018		149,638			492		$	13.34
Granted		61,848			—		$	9.00
Vested		(44,768	)		(481	)	$	11.30
Forfeited		(16,392	)		(2	)	$	13.28
Unvested at June 30, 2019		150,326			9		$	12.18

RSUs granted to employees before January 1, 2017 (“Pre-2017 RSUs”) included both service-based and performance conditions to vest in the underlying common stock. The performance condition related to Pre-2017 RSUs was satisfied on the effectiveness of the registration statement for our IPO, which occurred in March 2017. Total unrecognized compensation cost related to Pre-2017 RSUs was $94.6 million as of June 30, 2019 and is expected to be recognized over a weighted-average period of 1.2 years.

All RSUs granted after December 31, 2016 vest on the satisfaction of only a service-based condition (“Post-2017 RSUs”). Total unrecognized compensation cost related to Post-2017 RSUs was $1.3 billion as of June 30, 2019 and is expected to be recognized over a weighted-average period of 3.0 years. The service condition for Post-2017 RSUs granted prior to February 2018 is generally satisfied over four years, 10% after the first year of service, 20% over the second year, 30% over the third year, and 40% over the fourth year. In limited instances, we have issued Post-2017 RSUs with vesting periods in excess of four years. The service condition for Post-2017 RSUs granted after February 2018 is generally satisfied in equal monthly or quarterly installments over four years.

Additionally, we had 17.8 million and 22.4 million RSUs that were vested but have not yet settled as of June 30, 2019 and December 31, 2018, respectively. These RSUs are primarily related to the CEO award.

The following table summarizes the RSA activity during the six months ended June 30, 2019:

	Class A Outstanding RSAs			Weighted- Average Grant Date Fair Value per RSA
	(in thousands, except per share data)
Unvested at December 31, 2018		8,134		$	7.51
Granted		2,500		$	11.42
Vested		(1,567	)	$	10.68
Forfeited		(1,149	)	$	5.85
Unvested at June 30, 2019		7,918		$	8.36

The total fair value of RSAs vested during the six months ended June 30, 2019 and 2018 was $16.7 million and $6.3 million, respectively.

The following table summarizes the stock option award activity under the Stock Plans during the six months ended June 30, 2019:

	Class A Number of Shares			Class B Number of Shares			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value⁽¹⁾
	(in thousands, except per share data)
Outstanding at December 31, 2018		13,322			2,969		$	7.83		6.41	$	34,567
Granted		—			—		$	—		—	$	—
Exercised		(1,724	)		(790	)	$	2.76		—	$	—
Forfeited		(1,257	)		(29	)	$	13.89		—	$	—
Outstanding at June 30, 2019		10,341			2,150		$	8.22		5.77	$	78,348

Total unrecognized compensation cost related to unvested stock options was $27.7 million as of June 30, 2019 and is expected to be recognized over a weighted-average period of 2.1 years.

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
	(in thousands)
Cost of revenue	$	1,786	$	1,467	$	3,635	$	1,743
Research and development		132,610		92,303		244,852		170,118
Sales and marketing		26,474		21,996		44,234		38,182
General and administrative		34,704		40,605		65,409		79,587
Total	$	195,574	$	156,371	$	358,130	$	289,630