Fair Value Measurements - Schedule of Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Mar. 31, 2021	Mar. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment	$ 180,359	$ 188,978	$ 93,445
Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets held in Trust Account	1,521,021	1,609,575	1,968,107
Debt issued by Dermavant to NovaQuest	155,200	150,100	89,100
Liability instruments measured at fair value	5,906	67,893	102,373
Total liabilities at fair value	161,106	217,993	191,473
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets held in Trust Account	1,451,834	1,533,538	1,945,045
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets held in Trust Account	69,187	76,037	23,062
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt issued by Dermavant to NovaQuest	155,200	150,100	89,100
Liability instruments measured at fair value	5,906	67,893	102,373
Total liabilities at fair value	161,106	217,993	191,473
Money Market Funds [Member] \| Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	1,340,662	1,420,597	1,874,662
Money Market Funds [Member] \| Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	1,340,662	1,420,597	1,874,662
Other Investment [Member] \| Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment	11,935	11,129	8,880
Other Investment [Member] \| Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment	11,935	11,129	8,880
Sio Gene Therapies Inc [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment	50,700	48,500	45,300
Sio Gene Therapies Inc [Member] \| Common Stock [Member] \| Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment	50,716	48,487	45,329
Sio Gene Therapies Inc [Member] \| Common Stock [Member] \| Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment	50,716	48,487	45,329
Arbutus Biopharma Corporation [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment	117,700	129,400	39,200
Arbutus Biopharma Corporation [Member] \| Common Stock [Member] \| Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment	48,521	53,325	16,174
Arbutus Biopharma Corporation [Member] \| Common Stock [Member] \| Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment	48,521	53,325	16,174
Arbutus Biopharma Corporation [Member] \| Convertible Preferred Stock [Member] \| Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment	69,187	76,037	23,062
Arbutus Biopharma Corporation [Member] \| Convertible Preferred Stock [Member] \| Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment	$ 69,187	$ 76,037	$ 23,062

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

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Fair value as of the balance sheet date of derivative instrument not designated as hedging instrument and classified as a liability.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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Fair value of financial and nonfinancial obligations.

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