Related Party Transactions (Details)				1 Months Ended	3 Months Ended		6 Months Ended
		Aug. 01, 2020	Dec. 27, 2019 USD ($) director day	Aug. 31, 2020	Sep. 30, 2022 USD ($) $ / shares shares	Sep. 30, 2021 USD ($)	Sep. 30, 2022 USD ($) $ / shares shares	Sep. 30, 2021 USD ($)	Oct. 23, 2022 USD ($) $ / shares	Mar. 31, 2022 $ / shares
Related Party Transaction [Line Items]
Common shares par value (in USD per share) | $ / shares					$ 0.000017727		$ 0.000017727			$ 0.000017727
Interest expense	[1]				$ 4,813,000	$ 3,494,000	$ 9,013,000	$ 6,999,000
Expenses incurred under agreements					1,241,000	1,173,000	2,404,000	2,447,000
Subsequent Event
Related Party Transaction [Line Items]
Common shares par value (in USD per share) | $ / shares									$ 0.000017727
Subsequent Event | Sumitomo Pharma, Co., Ltd. | Myovant Sciences Ltd.
Related Party Transaction [Line Items]
Potential termination fee									$ 55,250,000
Majority Shareholder | Sunovion Pharmaceuticals Inc. Market Access Services Agreement
Related Party Transaction [Line Items]
Expenses incurred under agreements					$ 1,200,000	1,200,000	$ 2,400,000	2,400,000
Sumitomo 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					51.80%		51.80%
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 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 years
Sumitovant Biopharma, Inc. | Services Information Sharing Agreement
Related Party Transaction [Line Items]
Expenses incurred under agreements					$ 100,000		$ 100,000
MSG | Majority Shareholder | Sunovion Pharmaceuticals Inc. Market Access Services Agreement | Selling, General and Administrative Expenses
Related Party Transaction [Line Items]
Agreement term				2 years
Term Loan | Letter Agreement with Sumitomo Dainippon Pharma, Co., Ltd. | Sumitomo Pharma, Co., Ltd.
Related Party Transaction [Line Items]
Interest expense					4,813,000	2,885,000	8,445,000	5,789,000
Term Loan | Letter Agreement with Sumitomo Dainippon Pharma, Co., Ltd. | Sumitomo 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
Interest expense					$ 4,800,000	$ 2,900,000	$ 8,400,000	$ 5,800,000
LIBOR | Term Loan | Letter Agreement with Sumitomo Dainippon Pharma, Co., Ltd. | Sumitomo Pharma, Co., Ltd. | Majority Shareholder
Related Party Transaction [Line Items]
Variable interest rate (as a percent)			3.00%

[1] Includes $4,813 and $8,445 of interest expense under the Sumitomo Pharma Loan Agreement for the three and six months ended September 30, 2022, respectively. Includes $2,885 and $5,789 of interest expense under the Sumitomo Pharma Loan Agreement for the three and six months ended September 30, 2021, respectively. See Note 5(C).