Redeemable convertible preferred stock - Textual (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended			12 Months Ended
	Jun. 24, 2019	Dec. 31, 2018	Nov. 30, 2018	Jun. 30, 2018	Dec. 31, 2019	Dec. 31, 2018
Temporary Equity
Preferred Stock , shares issued		64,730,410			0	64,730,410
Preferred Stock , shares outstanding		64,730,410			0	64,730,410
Stock issuance cost						$ 449
Share Issued value under agreement					$ 95,453
Initial fair value of preferred stock tranche obligation in connection with the issuance of Series A Preferred Stock						7,350
Initial fair value of anti‑dilution right liability in connection with Amgen license agreement						$ 1,639
IPO
Temporary Equity
Preferred Stock , shares outstanding					0
Number of shares converted	21,056,136
Stock issuance cost	$ 2,942
Amgen Agreement
Temporary Equity
Initial fair value of anti‑dilution right liability in connection with Amgen license agreement			$ 7,404
Amgen Agreement | Amgen
Temporary Equity
Share Issued under agreement				2,653,333
Share Issued value under agreement				$ 1,353
Redeemable Convertible Preferred Stock
Temporary Equity
Number of shares converted	21,056,136				(64,730,410)
Beneficial conversion feature					$ 0
Series A Preferred Stock
Temporary Equity
Share Issued under agreement						17,653,333
Aggregate proceeds				14,784
Stock issuance cost				$ 216
Share Issued value under agreement						$ 8,787
Net Issuance cost						$ 216
Series B Preferred Stock
Temporary Equity
Share Issued under agreement		13,871,948				13,871,948
Original Issue price (in dollars per share)		$ 3.28				$ 3.28
Aggregate proceeds		$ 45,500
Share Issued value under agreement						$ 45,271
Net Issuance cost		$ 229				$ 229
First Tranche Closing | Series A Preferred Stock
Temporary Equity
Share Issued under agreement				15,000,000
Original Issue price (in dollars per share)				$ 1.00
Aggregate proceeds				$ 15,000
Preferred stock tranche obligation in connection with the issuance of Series A Preferred Stock					$ 7,350
Initial carrying value of stock issued				8,787
First Tranche Closing | Series A Preferred Stock | Amgen
Temporary Equity
Fair value of shares of Series A Preferred Stock issued to Amgen				1,353
Net Issuance cost				216
Initial fair value of preferred stock tranche obligation in connection with the issuance of Series A Preferred Stock				$ 7,350
Second Tranche Closing | Amgen Agreement | Amgen | Akero Therapeutics, Inc.
Temporary Equity
Ownership interest of the outstanding shares (as a percent)					10.00%
Second Tranche Closing | Series A Preferred Stock
Temporary Equity
Share Issued under agreement			25,000,001			25,000,001
Original Issue price (in dollars per share)			$ 1.00
Share Issued value under agreement						$ 24,996
Net Issuance cost			$ 4			$ 4
Preferred stock tranche obligation in associated with future purchase obligation			$ 32,750
Second Tranche Closing | Series A Preferred Stock | Amgen Agreement | Amgen
Temporary Equity
Share Issued under agreement			3,205,128
Initial fair value of anti‑dilution right liability in connection with Amgen license agreement			$ 7,404
Period prior to January 14, 2022
Temporary Equity
Share Issued under agreement					20,000