Nature of Business and Basis of Presentation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands					12 Months Ended
	Apr. 26, 2019	Apr. 12, 2019	Apr. 01, 2019	Apr. 02, 2018	Dec. 31, 2019	Dec. 31, 2018	Apr. 04, 2018
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Net proceeds from initial public offering after underwriting discounts and commissions and offering expenses						$ 150,843
Preferred stock, shares outstanding					0	0
Conversion of convertible preferred stock into common stock upon initial public offering, Shares				24,168,656
Proceeds from issuance of common stock in follow-on public offering, net of discounts and issuance costs					$ 134,524
Net loss					103,916	$ 55,577
Accumulated deficit					$ 199,674	$ 95,758
Common Stock
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Conversion of convertible preferred stock into common stock upon initial public offering, Shares						24,168,656
Initial Public Offering
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Shares issued and sold				10,350,000
Common stock at a public offering price							$ 16.00
Net proceeds from initial public offering after underwriting discounts and commissions and offering expenses				$ 150,800
Preferred stock, shares outstanding				0
Initial Public Offering | Common Stock
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Shares issued and sold						10,350,000
Common Stock, Preferred Stock, Debt Securities, Warrants and Units | Maximum
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Proceeds through future financings			$ 350,000
ATM
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Shares issued and sold					1,105,000
Common stock available for sale					76,800,000
ATM | Common Stock
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Shares issued and sold					1,105,000
Proceeds from issuance of common stock in follow-on public offering, net of discounts and issuance costs					$ 22,500
ATM | Maximum
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Proceeds through future financings			$ 100,000
Follow On Offering | Common Stock
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Shares issued and sold		5,555,556			6,388,889
Shares issued price per share		$ 22.50
Net proceeds after deducting underwriting discounts and commissions and offering expenses		$ 116,900
Underwriters Option | Common Stock
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Shares issued and sold	833,333
Shares issued price per share	$ 22.50
Net proceeds after deducting underwriting discounts and commissions and offering expenses	$ 17,600