Collaboration Agreements (Tables)

12 Months Ended

Dec. 31, 2021

Collaboration Agreement [Abstract]

Summary of Operating Expenses Category Related to Collaboration Agreement

The following table summarizes expenses related to the Biogen Collaboration Agreement that were incurred by the Company and the related reimbursement from Biogen, reflected by category of operating expenses:

	Year Ended December 31,
	2021
	(in thousands)
Expenses related to the Biogen Collaboration Agreement    incurred by Sage	$	193,776
Net reimbursement from Biogen reflected in the    consolidated statement of operations and comprehensive    loss:
Research and development expenses		(79,848	)
Selling, general and administrative expenses		(11,282	)
		(91,130	)
Total net expenses related to the Biogen Collaboration    Agreement in the consolidated statement of    operations and comprehensive income (loss)	$	102,646