Collaboration and License Agreements - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended		6 Months Ended		12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021	Jul. 31, 2020
Acceleron Collaboration Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Non refundable upfront payment received		$ 10,000			$ 10,000
Range of tiered royalties on net sales					mid single-digit percentage to a low double-digit percentage
Change in variable consideration constrained			$ 0		$ 0
Revenues			100	$ 2,300	1,000	$ 4,900
Deferred Revenue	$ 3,800		100	1,700	100	1,700	$ 600
Accounts Receivable, Related Parties			400		400		0
Deferred revenue current and non-current			0		0		600
Reimbursement Payment Received					4,600		3,900
Unbilled accounts receivable related to reimbursable research and development cost			100		100		700
Acceleron Collaboration Agreement | Research Milestones
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Non refundable upfront payment received	$ 2,000
Aggregate amount receivable on achievement of milestone			2,000		2,000
Amount received on achievement of milestone					2,000		2,000
Acceleron Collaboration Agreement | Research Milestones | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Aggregate amount receivable on achievement of milestone			18,500		18,500
Acceleron Collaboration Agreement | Clinical and Regulatory Milestones | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Aggregate amount receivable on achievement of milestone			202,500		202,500
Acceleron Collaboration Agreement | Worldwide Net Sales Milestones | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Aggregate amount receivable on achievement of milestone			217,500		217,500
MyoKardia Collaboration and License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Non refundable upfront payment received					10,000
Revenues			1,700	$ 2,000	3,500	$ 4,200
Deferred Revenue			1,000		1,000		2,300
Accounts Receivable, Related Parties			0		0		2,500
Deferred revenue current and non-current			1,800		1,800		4,100
Reimbursement Payment Received					4,100		3,200
Unbilled accounts receivable related to reimbursable research and development cost			700		700		500
Upfront payment								$ 10,000
Payment for prepaid research funding			2,500		2,500			2,500
Prepaid research funding payment received			2,500		2,500
MyoKardia Collaboration and License Agreement | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payment for certain identified targets								298,500
Milestone payment for certain other identified targets								$ 150,000
MyoKardia Collaboration and License Agreement | Clinical and Regulatory Milestones
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Aggregate amount receivable on achievement of milestone			$ 2,500		$ 2,500		$ 2,500