Description of the Business - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands				17 Months Ended
	May 21, 2020	Feb. 12, 2019	Jan. 04, 2018	Feb. 28, 2019	Jun. 30, 2020	Dec. 31, 2019
Description Of Business [Line Items]
Issuance of common stock in connection with a public offering, net of underwriting discounts, commissions, and offering costs, shares	9,433,963
Offering price, per share	$ 13.25
Accumulated deficit					$ (455,114)	$ (334,170)
Funds raised through Series A and Series B Convertible Preferred Stock, convertible note financings and completed IPO				$ 942,000
AA Biopharma Inc.
Description Of Business [Line Items]
Cash received in connection with acquisition			$ 12,800
5.00% Convertible Senior Notes Due 2027
Description Of Business [Line Items]
Debt instrument interest rate percentage	5.00%				5.00%
Initial Public Offering ("IPO")
Description Of Business [Line Items]
Issuance of common stock in connection with a public offering, net of underwriting discounts, commissions, and offering costs, shares		19,837,500
Offering price, per share		$ 16.00
Net proceeds, after deducting underwriting discounts, commissions, and offering expenses		$ 291,300
Initial Public Offering ("IPO") | Conversion of Convertible Preferred Stock into Common Stock
Description Of Business [Line Items]
Common stock issued in conversion of convertible preferred stock		30,493,460