Leases, Commitments and Contingencies - CyDex License Agreement - Additional Information (Detail) - USD ($)	12 Months Ended			88 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2022
Commitments And Contingencies [Line Items]
Research and development expense	$ 326,163,000	$ 283,166,000	$ 292,714,000
CyDex License Agreement [Member]
Commitments And Contingencies [Line Items]
Research and development expense				$ 1,000,000.0
CyDex License Agreement [Member] | First and Second Clinical Development Milestones [Member] | Brexanolone [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	800,000			800,000
CyDex License Agreement [Member] | First and Second Regulatory Milestones [Member] | Brexanolone [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	3,800,000			3,800,000
CyDex License Agreement [Member] | Third and Fourth Clinical Development Milestones [Member] | Brexanolone [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	1,300,000			1,300,000
CyDex License Agreement [Member] | Third and Fourth Regulatory Milestones [Member] | Brexanolone [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	8,500,000			8,500,000
CyDex License Agreement [Member] | Clinical Development [Member] | SAGE-689 [Member]
Commitments And Contingencies [Line Items]
Research and development expense		100,000	$ 1,300,000
CyDex License Agreement [Member] | Clinical Development [Member] | SAGE-689 [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	800,000			800,000
CyDex License Agreement [Member] | Regulatory Milestones [Member]
Commitments And Contingencies [Line Items]
Construction Expense Related To Milestone Payment		$ 1,300,000
CyDex License Agreement [Member] | Regulatory Milestones [Member] | SAGE-689 [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	1,800,000			1,800,000
CyDex License Agreement [Member] | Clinical Development and Regulatory Milestones [Member]
Commitments And Contingencies [Line Items]
Research and development expense related to milestone expense				3,600,000
Milestone payments				3,600,000
Intangible asset related to milestone	$ 3,000,000.0			$ 3,000,000.0