Stock Plan and Stock-Based Compensation - Additional Information (Details) - USD ($)			3 Months Ended	12 Months Ended
	Jan. 01, 2020	Jan. 01, 2019	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized employee compensation costs				$ 23,700,000
Non-vested stock option recognized weighted average period				2 years 10 months 24 days
Intrinsic value of shares exercised				$ 200,000	$ 600,000
Fair value of shares vested				$ 7,800,000	$ 3,000,000
Total shares of authorized common stock reserved for future issuance				8,310,754	5,259,271
Common stock, shares outstanding				45,925,004	44,537,946
Share-based compensation, vested stock options				372,774	14,918
Description of expected term simplified method				The Company has opted to use the “simplified method” for estimating the expected term of options, whereby the expected term equals the arithmetic average of the vesting term and the original contractual term of the option (generally 10 years).
Expected term				10 years
Expected dividend yield				0.00%
Non-Employee Stock-Based Compensation
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares not vested and subject to repurchase				308,596	31,388
Stock based compensation expense				$ 900,000	$ 300,000
Restricted Stock Agreements
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period						4 years
Estimated fair value, price per share						$ 0.0004
Vesting interval period						monthly
Chief Executive Officer and President | Restricted Stock Agreements
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares issued						2,777,776
Price per share						$ 0.0004
2018 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares issued or transferred			3,570,000
Total shares of authorized common stock reserved for future issuance				2,315,099
2018 Equity Incentive Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares of common stock reserved for issuance under evergreen provision		3,570,000
Percentage of common stock outstanding		4.00%
2018 Equity Incentive Plan | Subsequent Event
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares of common stock reserved for issuance under evergreen provision	1,837,000
2015 Stock Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares not vested and subject to repurchase				455,158	927,123
Cash received from early exercise of unvested options				$ 1,700,000	$ 2,800,000
Award vesting period				48 months
Total shares of authorized common stock reserved for future issuance			709,558
2018 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Purchase date of fair market value trading days			24 months
Total shares of authorized common stock reserved for future issuance			714,000	933,273
2018 Employee Stock Purchase Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Purchase price of common stock as percentage of market value			85.00%
Number of shares of common stock that may be purchased by an employee on any purchase date			3,000
Number of shares that may be purchased in any calendar year			$ 25,000
Percentage of common stock shares outstanding		1.00%
Common stock, shares outstanding		1,071,000
2018 Employee Stock Purchase Plan | Subsequent Event
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares of common stock reserved for issuance under evergreen provision	459,250