Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2021

Share-based Payment Arrangement [Abstract]

Stock-based compensation expense included in the consolidated statements of operations was as follows:


	Year Ended December 31,
(in thousands)	2021		2020		2019
Cost of revenue	$	4,446	$	3,158	$	2,817
Sales and marketing	29,410		19,842		16,032
Research and development	20,593		14,794		8,911
General and administrative	24,956		21,779		15,683
Total stock-based compensation expense	$	79,405	$	59,573	$	43,443

Summary of Restricted Stock and Restricted Stock Units

A summary of our restricted stock and RSU activity is presented below:


	Restricted Stock			RSUs
(in thousands, except for per share data)	Number of Shares	Weighted Average Grant Date Fair Value		Number of Shares	Weighted Average Grant Date Fair Value
Unvested balance at December 31, 2018	890	$	4.25	1,129	$	18.90
Granted	—	—		2,715	27.81
Vested	(395)	4.25		(479)	18.28
Forfeited	—	—		(471)	25.21
Unvested balance at December 31, 2019	495	4.25		2,894	26.34
Granted	—	—		3,570	28.23
Vested	(396)	4.25		(1,504)	25.37
Forfeited	—	—		(470)	26.68
Unvested balance at December 31, 2020	99	4.25		4,490	28.13
Granted	—	—		3,842	43.57
Vested	(99)	4.25		(1,872)	28.14
Forfeited	—	—		(679)	33.64
Unvested balance at December 31, 2021	—	—		5,781	37.74

Stock Option Activity

A summary of our stock option activity is below:


(in thousands, except for per share data and years)	Number of Shares	Weighted Average Exercise Price		Weighted-Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value
Outstanding at December 31, 2018	19,219	$	7.78	8.0	$	277,114
Granted	—	—
Exercised	(4,205)	4.53			98,378
Forfeited/canceled	(2,075)	10.63
Outstanding at December 31, 2019	12,939	8.38		7.1	201,608
Granted	—	—
Exercised	(2,956)	7.34			73,277
Forfeited/canceled	(542)	10.80
Outstanding at December 31, 2020	9,441	8.56		6.4	412,547
Granted	—	—
Exercised	(2,671)	6.84			111,256
Forfeited/canceled	(39)	14.96
Outstanding at December 31, 2021	6,731	9.21		5.5	308,677
Exercisable at December 31, 2021	5,851	8.30		5.4	273,642

Schedule of Share-based Payment Award, Employee Stock Purchase Plan, Valuation Assumptions

The fair value of the 2018 ESPP purchase rights was estimated on the offering or modification dates using a Black-Scholes option-pricing model and the following assumptions:


	Year Ended December 31,
	2021	2020	2019
Expected term (in years)	0.5 — 2.0	0.5 — 2.0	0.5 — 2.0
Expected volatility	37.2% — 59.4%	41.6% — 60.1%	34.4% — 44.6%
Risk-free interest rate	0.1% — 0.2%	0.1% — 0.9%	1.5% — 2.5%
Expected dividend yield	—	—	—