Fair value of financial assets and liabilities (Tables)

12 Months Ended

Dec. 31, 2019

Fair value of financial assets and liabilities

Summary of assets that are measured at fair value on a recurring basis

	Fair Value Measurements as of December 31, 2019 Using:
	Total		Level 1		Level 2		Level 3
Money market funds	$	49,948	$	49,948	$	—	$	—
Commercial paper		49,114		—		49,114		—
U.S. treasury securities		6,048		6,048		—		—
Corporate debt securities		20,143		—		20,143		—
	$	125,253	$	55,996	$	69,257	$	—

Schedule of roll forward of the fair values of the Company’s preferred stock tranche obligation and anti‑dilution right liability

	Preferred stock		Anti‑dilution
	tranche		right
	obligation		liability
Balance as of December 31, 2017	$	—	$	—
Initial fair value of anti‑dilution right liability in connection with Amgen license agreement		—		1,639
Initial fair value of preferred stock tranche obligation in connection with the issuance of Series A Preferred Stock		7,350		—
Change in fair value		62,150		5,765
Settlement of future purchase obligation		(32,750)		—
Settlement of anti‑dilution right liability upon issuance of Series A preferred stock		—		(7,404)
Extinguishment of call option liability		(36,750)		—
Balance as of December 31, 2018	$	—	$	—