License and Collaboration Agreements - Additional Information (Details) - USD ($)	1 Months Ended		3 Months Ended		9 Months Ended
	Aug. 31, 2020	Jul. 31, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Aug. 11, 2020	Jul. 31, 2019
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Fair value of warrant							$ 18,700,000
Consideration due from related party			$ 35,000,000		$ 35,000,000
Research and development			$ 59,074,000	$ 47,372,000	$ 155,286,000	$ 101,270,000
Exclusive License Agreement \| LianBio Licencising,, LLC.
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from license fees received	$ 40,000,000.0
Additional proceeds from license fees received	$ 35,000,000.0
Financing event occurring date	Oct. 29, 2020
Number of warrants	170,000
Warrants exercise price	$ 275.00
Percentage of ordinary shares represents warrants	17.00%
Fair value of warrant	$ 18,700,000
Negotiation period	90 days
Exclusive License Agreement \| LianBio Licencising,, LLC. \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Regulatory milestone payments	$ 60,000,000.0
Sales milestone payments	$ 87,500,000
Exclusive License Agreement \| LianBio Licencising,, LLC.
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of ordinary shares represents warrants	17.00%
Fair value of warrant	$ 18,700,000
Total consideration	93,700,000
Cash consideration	40,000,000.0
Consideration due from related party non-current	35,000,000.0
Consideration due from related party	$ 35,000,000.0
Multi-Target Collaboration and License Agreement \| Fulcrum Therapeutics Inc
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payment of license fees		$ 10,000,000.0
Prepaid research funding at close of transaction		2,500,000
Milestone payments eligible for additional cardiomyopathy target		298,500,000
Research and development		10,000,000.0
Multi-Target Collaboration and License Agreement \| Fulcrum Therapeutics Inc \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research, development and commercial milestone payments and additional research reimbursements		302,500,000
Milestone payments eligible for a follow-on target		$ 150,000,000.0
Termination Agreement \| Sanofi (Aventis Inc.) \| Royalty Rights
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount Payable to reacquire research and development asset								$ 80,000,000.0

MyoKardia, Inc. 10-Q