Equity Incentive Plans (Tables)

12 Months Ended

Dec. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Fair Value of Stock Option Award Granted

The following assumptions were used to estimate the fair value of stock option awards granted to employees under the Company’s equity incentive plans and the shares purchasable under the ESPP during the periods presented:

	Year Ended December 31,
	2019	2018	2017
Employee Stock Options
Expected term (in years)	4.6 - 6.1	5.3 - 6.1	N/A
Risk-free interest rate	1.38% - 2.58%	2.65% - 2.96%	N/A
Volatility	70.25% - 86.92%	69.13% - 77.62%	N/A
Dividend yield	–	–	N/A
Employee Stock Purchase Plan
Expected term (in years)	0.49 - 1.99	N/A	N/A
Risk-free interest rate	1.46% - 1.87%	N/A	N/A
Volatility	72.08% - 78.70%	N/A	N/A
Dividend yield	–	N/A	N/A

Summary of Stock Option Activity

Stock Options

The following table summarizes stock option activity for the years ended December 31, 2019 and 2018:

	Shares Subject to Options Outstanding					Weighted- Average
				Weighted-		Remaining
				Average Exercise		Contractual Life		Aggregate
	Shares			Price		(Years)		Intrinsic Value
								(in thousands)
Outstanding as of December 31, 2017		—			—		—	$	—
Options granted		5,143,551		$	7.49
Option exercised		—		$	—
Options forfeited/cancelled		(36,222	)	$	4.85
Outstanding as of December 31, 2018		5,107,329		$	7.51		9.7	$	16,343
Options granted		4,194,624		$	20.11
Option exercised		(419,593	)	$	4.87
Options forfeited/cancelled		(344,300	)	$	11.64
Outstanding as of December 31, 2019		8,538,060		$	13.67		9.0	$	35,385
Options vested and exercisable as of December 31,    2019		1,215,471		$	7.25		8.7	$	10,183

Summary of Restricted Stock Activity

The summary of the Company’s restricted stock activity during the years ended December 31, 2019, 2018 and 2017 is as follows:

	Number of			Weighted-
	Restricted			Average
	Stock Units			Grant Date
	Outstanding			Fair Value
Nonvested at December 31, 2016		—		$	—
Granted		1,305,421			0.09
Nonvested at December 31, 2017		1,305,421		$	0.09
Granted		8,673,584			5.53
Vested		(2,369,696	)		7.58
Forfeited		(127,277	)		0.09
Nonvested at December 31, 2018		7,482,032		$	4.01
Granted		—			—
Vested		(2,833,506	)		4.05
Forfeited		—			—
Nonvested at December 31, 2019		4,648,526		$	3.98

Stock-Based Compensation Expense Reported in Condensed Consolidated Statements of Operations

Stock-based compensation expense has been reported in the Company’s consolidated statements of operations as follows (in thousands):

	Year Ended
	December 31,
	2019		2018		2017
Research and development	$	10,227	$	679	$	17
General and administrative		10,592		30,268		15
Total stock-based compensation	$	20,819	$	30,947	$	32