Stock-Based Compensation (Tables)

6 Months Ended

Jun. 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 June 30,				Six Months Ended June 30,
(in thousands)	2020		2019		2020		2019
Cost of revenue	$	830	$	742	$	1,577	$	1,394
Sales and marketing	5,375		4,215		9,871		7,581
Research and development	3,893		2,441		6,841		4,471
General and administrative	5,568		3,975		10,412		7,246
Total stock-based compensation expense	$	15,666	$	11,373	$	28,701	$	20,692

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	—		—		3,372		27.86
Vested	(198	)	4.25		(569	)	29.04
Forfeited	—		—		(261	)	25.71
Unvested balance at June 30, 2020	297		4.25		5,436		27.03

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	(1,594)	6.89			33,416
Forfeited/canceled	(287)	10.99
Outstanding at June 30, 2020	11,058	8.53		6.8	235,370
Exercisable at June 30, 2020	6,692	6.42		6.4	156,517

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:

	Six Months Ended June 30,
	2020	2019
Expected term (in years)	0.5 — 2.0	0.5 — 2.0
Expected volatility	41.6% — 47.9%	35.4% — 44.6%
Risk-free interest rate	0.8% — 0.9%	2.5% — 2.6%
Expected dividend yield	—	—