Collaboration and License Agreements - Additional Information (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Jul. 31, 2020
Acceleron Collaboration Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Non refundable upfront payment received	$ 10,000,000.0				$ 10,000,000.0
Range of tiered royalties on net sales	mid single-digit percentage to a low double-digit percentage
Change in variable consideration constrained	$ 0
Revenues	900,000	$ 2,600,000
Deferred Revenue			$ 500,000	$ 2,100,000
Accounts Receivable, Related Parties	0		0
Deferred revenue current and non-current	100,000		600,000
Reimbursement Payment Received	4,600,000		3,900,000
Unbilled accounts receivable related to reimbursable research and development cost	400,000		700,000
Acceleron Collaboration Agreement | Research Milestones
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Non refundable upfront payment received				$ 2,000,000.0
Aggregate amount receivable on achievement of milestone	2,000,000.0
Amount received on achievement of milestone	2,000,000.0		2,000,000.0
Acceleron Collaboration Agreement | Research Milestones | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Aggregate amount receivable on achievement of milestone	18,500,000
Acceleron Collaboration Agreement | Clinical and Regulatory Milestones | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Aggregate amount receivable on achievement of milestone	202,500,000
Acceleron Collaboration Agreement | Worldwide Net Sales Milestones | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Aggregate amount receivable on achievement of milestone	217,500,000
MyoKardia Collaboration and License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Non refundable upfront payment received	10,000,000.0
Revenues	1,700,000	$ 2,200,000
Deferred Revenue			1,300,000
Accounts Receivable, Related Parties	0		2,500,000
Deferred revenue current and non-current	2,800,000		4,100,000
Reimbursement Payment Received	3,700,000		3,200,000
Unbilled accounts receivable related to reimbursable research and development cost	400,000		500,000
Upfront payment						$ 10,000,000.0
Payment for prepaid research funding	2,500,000					2,500,000
Prepaid research funding payment received	2,500,000
MyoKardia Collaboration and License Agreement | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payment for certain identified targets						298,500,000
Milestone payment for certain other identified targets						$ 150,000,000.0
MyoKardia Collaboration and License Agreement | Clinical and Regulatory Milestones
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Aggregate amount receivable on achievement of milestone	$ 2,500,000		$ 2,500,000