Related Party Transactions (Narrative) (Details)						1 Months Ended	12 Months Ended
		Aug. 05, 2020 USD ($)	Aug. 01, 2020	Dec. 30, 2019 USD ($)	Dec. 27, 2019 USD ($) day director shares	Aug. 31, 2020	Mar. 31, 2022 USD ($) shares	Mar. 31, 2021 USD ($)	Mar. 31, 2020 USD ($)
Related Party Transaction [Line Items]
Proceeds from related party debt financing							$ 0	$ 245,000,000	$ 113,700,000
Interest expense	[1]						13,971,000	10,401,000	12,663,000
Majority Shareholder | Sunovion Pharmaceuticals Inc. Market Access Services Agreement | SG&A expense
Related Party Transaction [Line Items]
Expenses incurred under agreements							$ 4,842,000	5,330,000
Sumitomo Dainippon Pharma Co., Ltd. | Majority Shareholder
Related Party Transaction [Line Items]
Number of shares owned (in shares) | shares					45,008,604		50,041,181
Ownership percentage					50.20%		52.80%
Ownership threshold for appointment of directors (as a percent)					50.00%
Number of independent directors required for audit committee | director					3
Ownership threshold for voting rights (as a percent)					60.00%
Ownership threshold for right of ownership percentage maintenance					50.00%
Sumitomo Dainippon Pharma Co., Ltd. | Majority Shareholder | Sumitovant Other Expenses Agreement | SG&A expense
Related Party Transaction [Line Items]
Expenses incurred under agreements								800,000
Sumitomo Dainippon Pharma Co., Ltd. | Majority Shareholder | Sumitovant Other Expenses Agreement | R&D expense
Related Party Transaction [Line Items]
Expenses incurred under agreements							$ 100,000	700,000
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
Roivant | Majority Shareholder | Service Agreement
Related Party Transaction [Line Items]
Expenses incurred under agreements									600,000
MSG | Majority Shareholder | Sunovion Pharmaceuticals Inc. Market Access Services Agreement
Related Party Transaction [Line Items]
Expenses incurred under agreements								3,800,000
MSG | Majority Shareholder | Sunovion Pharmaceuticals Inc. Market Access Services Agreement | SG&A expense
Related Party Transaction [Line Items]
Expenses incurred under agreements							4,800,000	3,700,000
Agreement term						2 years
MSG | Majority Shareholder | Sunovion Pharmaceuticals Inc. Market Access Services Agreement | R&D expense
Related Party Transaction [Line Items]
Expenses incurred under agreements							0	58,000
Term Loan | Letter Agreement with Sumitomo Dainippon Pharma, Co., Ltd.
Related Party Transaction [Line Items]
Proceeds from related party debt financing				$ 113,700,000
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
Outstanding balance							358,700,000
Interest expense							$ 11,551,000	$ 9,766,000	$ 1,441,000
Term Loan | New Letter Agreement with Sumitomo Dainippon Pharma, Co., Ltd. | Sumitomo Dainippon Pharma Co., Ltd. | Majority Shareholder
Related Party Transaction [Line Items]
Maximum borrowing commitment		$ 200,000,000
Facility term		5 years
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 $11,551, $9,766, and $1,441 of interest expense under the Sumitomo Pharma Loan Agreement for the years ended March 31, 2022, 2021, and 2020, respectively