Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2019

Share-based Payment Arrangement [Abstract]

Stock-based compensation expense

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

	Year Ended December 31,
(in thousands)	2019		2018		2017
Cost of revenue	$	2,817	$	1,707	$	281
Sales and marketing	16,032		6,911		1,579
Research and development	8,911		5,804		1,782
General and administrative	15,683		8,453		4,118
Total stock-based compensation expense	$	43,443	$	22,875	$	7,760

Stock option activity

A summary of our stock option activity for the periods presented 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, 2016	9,336	$	2.77	7.2	$	15,374
Granted	9,022	5.22
Exercised	(1,870)	1.62			7,667
Forfeited/canceled	(1,915)	3.21
Outstanding at December 31, 2017	14,573	4.38		8.2	77,020
Granted	6,108	15.17
Exercised	(740)	2.26			9,902
Forfeited/canceled	(722)	7.23
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
Exercisable at December 31, 2019	6,473	6.04		6.4	116,016

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,
	2019	2018
Expected term (in years)	0.5 — 2.0	0.6 — 2.1
Expected volatility	34.4% — 44.6%	31.9% — 33.5%
Risk-free interest rate	1.5% — 2.5%	2.3% — 2.7%
Expected dividend yield	—	—

The fair value of each stock option was estimated on the grant date based on the following assumptions:

	Year Ended December 31,
	2018	2017
Expected term (in years)	6.3	6.3
Expected volatility	41.3% — 43.3%	45.2% — 47.0%
Risk-free interest rate	2.7% — 2.9%	1.9% — 2.4%
Expected dividend yield	—	—
Expected forfeiture rate	—	—

Summary of restricted stock and restricted stock units

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

	Restricted Stock				Restricted Stock Units
(in thousands, except for per share data and years)	Number of Shares		Weighted Average Grant Date Fair Value		Number of Shares		Weighted Average Grant Date Fair Value
Unvested balance at December 31, 2016	—		$	—	—		$	—
Granted	1,583		4.25		—		—
Vested	—		—		—		—
Forfeited	—		—		—		—
Unvested balance at December 31, 2017	1,583		4.25		—		—
Granted	—		—		1,200		18.75
Vested	(693	)	4.25		—		—
Forfeited	—		—		(71	)	16.27
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