Equity Incentive Plans (Tables)

12 Months Ended

Dec. 31, 2019

Share-based Payment Arrangement, Disclosure [Abstract]

Summary of the Company's stock option activity

A summary of the Company’s stock option activity under the Plans is as follows:

	Outstanding Options			Weighted- Average Exercise Price		Weighted- Average Remaining Terms (Years)		Aggregate Intrinsic Value
Balance as of December 31, 2018		14,264,376		$	1.91		8.2	$	71,902,234
Granted		4,785,842		$	19.05
Exercised		(2,226,493	)	$	1.69
Cancelled		(905,482	)	$	6.71
Balance as of December 31, 2019		15,918,243		$	6.82		7.9	$	1,105,222,370

	Outstanding Options		Weighted- Average Exercise Price		Weighted- Average Remaining Terms (Years)		Aggregate Intrinsic Value
Vested and exercisable as of December 31, 2019		7,362,304	$	1.96		6.9	$	546,973,399
Unvested and exercisable as of December 31, 2019		1,138,439	$	5.90		8.3	$	80,094,346

Summary of restricted shares issued under stock plan

A summary of these restricted shares issued under the 2012 Stock Plan is as follows:

	Number of Shares			Weighted- Average Exercise Price
Outstanding and unvested as of December 31, 2018		232,750		$	2.80
Exercised		29,000		$	11.48
Vested		(123,500	)	$	3.98
Outstanding and unvested as of December 31, 2019		138,250		$	3.57

Stock Option Valuation Assumptions

The fair value of each employee option grant was estimated on the date of grant using the Black-Scholes option pricing model and the following assumptions for the periods indicated:

	Year Ended December 31,
	2019	2018	2017
Expected volatility	40% – 53%	45% – 46%	45% – 48%
Risk-free interest rate	1.5% – 2.5%	2.7% – 3.1%	1.9% – 2.3%
Expected term	5.0 – 6.9 years	5.3 – 6.5 years	4.2 – 6.5 years
Expected dividend	—  %	—  %	—  %

Schedule of Fair value of the Employee Stock Purchase Plan

For the year ended December 31, 2019, the fair value of the ESPP was estimated using the following assumptions.

	Year Ended December 31,
	2019
Expected volatility	52%
Risk-free interest rate	1.85%
Expected term	0.7 years
Expected dividend	—  %

Recorded stock-based compensation expense in the condensed consolidated statement of operations

The Company recorded stock-based compensation expense in the consolidated statement of operations for the periods presented as follows (in thousands):

	Year Ended December 31,
	2019		2018		2017
Cost of revenue	$	325	$	85	$	44
Research and development		5,721		1,030		801
Selling, general and administrative		7,287		1,543		816
Total stock-based compensation expense	$	13,333	$	2,658	$	1,661