Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2019

Stockholders' Equity Note [Abstract]

Schedule of Stock Option Activity

The following table summarizes stock option activity during the year ended December 31, 2019:

	Number of Shares		Weighted-Average  Exercise Price		Weighted-Average Remaining Contractual Term	Aggregate Intrinsic Value
	(in thousands)				(in years)	(in thousands)
Outstanding at January 1, 2017	8,467		$	1.54	8.5	$	7,480
Granted	3,008		2.90
Exercised	(414	)	1.48
Cancelled/forfeited	(691	)	1.88
Outstanding at December 31, 2017	10,370		1.92		8.0	$	16,901
Granted	3,984		5.32
Exercised	(1,264	)	2.10
Cancelled/forfeited	(880	)	2.64
Outstanding at December 31, 2018	12,210		2.96		7.8	$	64,590
Granted	2,516		10.87
Exercised	(2,650	)	2.45
Cancelled/forfeited	(807	)	5.10
Outstanding at December 31, 2019	11,269		$	4.68	7.3	$	173,471
Vested and exercisable at December 31, 2019	6,994		$	2.68	6.5	$	121,610

Schedule of Unvested Exercised Options

The activity of non-vested shares as a result of early exercise of options granted to employees and non-employees, is as follows:

	Year ended December 31,
	2019		2018		2017
	(in thousands)
Beginning balance	245		138		597
Early exercise of options	117		238		2
Vested	(162	)	(120	)	(461	)
Repurchased	—		(11	)	—
Ending balance	200		245		138

Employee Stock Options, Valuation Assumptions

We estimated the fair value of stock option awards during the years ended December 31, 2019, 2018, and 2017 on the date of the grant using the Black-Scholes option pricing model with the following weighted-average assumptions:

	Year ended December 31,
	2019	2018	2017
Fair value of common stock	$8.24 - $22.70	$3.86 - $8.16	$2.98 - $3.58
Expected term (in years)	6.02	6.02	5.96
Risk-free interest rate	1.55% - 2.5%	2.62% - 3.0%	1.9% - 2.1%
Expected volatility	39.1% - 42.7%	40.2% - 41.5%	41% - 45%
Dividend yield	—%	—%	—	%

Schedule of Restricted Stock Units

The following table summarizes RSU activity during the year ended December 31, 2019:

	Number of Shares		Weighted-Average  Grant Date Fair Value Per Share
	(in thousands)
Nonvested RSUs as of December 31, 2018	—		$	—
Granted	1,644		20.07
Cancelled/forfeited	(3	)
Nonvested RSUs as of December 31, 2019	1,641		$	20.07

Employee Stock Purchase Plan, Valuation Assumptions

We estimated the fair value of shares granted under the ESPP on the first date of the offering period using the Black-Scholes option pricing model with the following assumptions:

	Year ended December 31,
	2019	2018
Fair value of common stock	$6.02 - $6.92	N/A
Expected term (in years)	0.47-0.50	N/A
Risk-free interest rate	1.59% - 2.35%	N/A
Expected volatility	36% - 43%	N/A
Dividend yield	—%	N/A

Schedule of Stock-Based Compensation Expense

The following table summarizes the components of total stock-based compensation expense included in the accompanying Consolidated Statements of Operations:

	Year ended December 31,
	2019		2018		2017
	(in thousands)
Stock-based compensation expense by caption:
Cost of revenue	$	1,410	$	265	$	190
Research and development	2,920		1,332		1,040
Sales and marketing	3,497		1,023		493
General and administrative	4,318		1,459		1,086
Total	$	12,145	$	4,079	$	2,809