Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2020

Share-based Payment Arrangement [Abstract]

Stock-based compensation expense

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

	Three Months Ended September 30,				Nine Months Ended September 30,
(in thousands)	2020		2019		2020		2019
Cost of revenue	$	826	$	694	$	2,403	$	2,088
Sales and marketing	4,806		3,521		14,677		11,102
Research and development	3,953		2,124		10,794		6,595
General and administrative	5,715		4,160		16,127		11,406
Total stock-based compensation expense	$	15,300	$	10,499	$	44,001	$	31,191

Summary of restricted stock and restricted stock units

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

	Restricted Stock			Restricted Stock Units
(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, 2019	495	$	4.25	2,894	$	26.34
Granted	—	—		3,453	28.01
Vested	(297)	4.25		(1,134)	24.78
Forfeited	—	—		(424)	26.70
Unvested balance at September 30, 2020	198	4.25		4,789	27.88

Stock option activity

A summary of our stock option activity is presented below:

(in thousands, except for exercise prices and years)	Number of Shares	Weighted Average Exercise Price		Weighted-Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value
Outstanding at December 31, 2019	12,939	$	8.38	7.1	$	201,608
Granted	—	—
Exercised	(2,366)	6.67			55,734
Forfeited/canceled	(541)	10.80
Outstanding at September 30, 2020	10,032	8.65		6.6	291,925
Exercisable at September 30, 2020	6,281	6.62		6.3	195,518

ESPP 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:

	Nine Months Ended September 30,
	2020	2019
Expected term (in years)	0.5 — 2.0	0.5 — 2.0
Expected volatility	41.6% — 60.1%	34.4% — 44.6%
Risk-free interest rate	0.1% — 0.9%	1.5% — 2.5%
Expected dividend yield	—	—