Related Party Transactions (Details)				1 Months Ended	3 Months Ended		9 Months Ended
		Aug. 01, 2020	Dec. 27, 2019 USD ($) day director	Aug. 31, 2020	Dec. 31, 2021 USD ($) shares	Dec. 31, 2020 USD ($)	Dec. 31, 2021 USD ($) shares	Dec. 31, 2020 USD ($)
Related Party Transaction [Line Items]
Interest expense	[1]				$ 3,479,000	$ 2,609,000	$ 10,478,000	$ 6,908,000
Sumitomo Dainippon Pharma Co., Ltd. | Majority Shareholder
Related Party Transaction [Line Items]
Number of shares owned (in shares) | shares					50,041,181		50,041,181
Ownership percentage					53.40%		53.40%
Ownership threshold for appointment of directors			50.00%
Number of independent directors required for audit committee | director			3
Ownership threshold for voting rights			60.00%
Ownership threshold for right of ownership percentage maintenance			50.00%
Sumitomo Dainippon Pharma Co., Ltd. | Majority Shareholder | Sumitovant Other Expenses Agreement | Selling, General and Administrative Expenses
Related Party Transaction [Line Items]
Expenses incurred under agreements						200,000		500,000
Sumitomo Dainippon Pharma Co., Ltd. | Majority Shareholder | Sunovion Pharmaceuticals Inc. Market Access Services Agreement
Related Party Transaction [Line Items]
Agreement term		3 years
Agreement extension term		1 year
Termination notice period		9 months
MSG | Majority Shareholder | Sunovion Pharmaceuticals Inc. Market Access Services Agreement | Selling, General and Administrative Expenses
Related Party Transaction [Line Items]
Agreement term				2 years
Expenses incurred under agreements					$ 1,337,000	1,400,000	$ 3,784,000	2,500,000
Term Loan | Letter Agreement with Sumitomo Dainippon Pharma, Co., Ltd. | Sumitomo Dainippon Pharma Co., Ltd.
Related Party Transaction [Line Items]
Interest expense					2,871,000	$ 2,569,000	8,660,000	$ 6,868,000
Term Loan | Letter Agreement with Sumitomo Dainippon Pharma, Co., Ltd. | Sumitomo Dainippon Pharma Co., Ltd. | Majority Shareholder
Related Party Transaction [Line Items]
Maximum borrowing commitment			$ 400,000,000
Facility term			5 years
Notice period for prepayment | day			10
Default interest rate (as a percent)			5.00%
Repayment period upon change in control			30 days
Available borrowing capacity					41,300,000		41,300,000
Outstanding balance					$ 358,700,000		$ 358,700,000
LIBOR | Term Loan | Letter Agreement with Sumitomo Dainippon Pharma, Co., Ltd. | Sumitomo Dainippon Pharma Co., Ltd. | Majority Shareholder
Related Party Transaction [Line Items]
Variable interest rate (as a percent)			3.00%

[1] Includes $2,871 and $8,660 of interest expense under the Sumitomo Dainippon Pharma Loan Agreement for the three and nine months ended December 31, 2021, respectively. Includes $2,569 and $6,868 of interest expense under the Sumitomo Dainippon Pharma Loan Agreement for the three and nine months ended December 31, 2020, respectively (see Note 5).