Stockholders' Equity - Additional Information (Detail)			1 Months Ended			3 Months Ended			6 Months Ended
	Sep. 17, 2020 shares	May 14, 2020 tradingDay $ / shares	Sep. 30, 2020 USD ($) $ / shares shares	May 31, 2020 USD ($) $ / shares shares	Apr. 30, 2020 USD ($) $ / shares shares	Sep. 30, 2020 USD ($) $ / shares shares	Jun. 30, 2020 shares	[1]	Sep. 30, 2020 USD ($) $ / shares shares	Sep. 30, 2019 USD ($)	Mar. 31, 2020 $ / shares shares	May 31, 2019 $ / shares shares
Subsidiary or Equity Method Investee [Line Items]
Preferred stock, issued (in shares)			0			0			0		0
Preferred stock, outstanding (in shares)			0			0			0		0
Preferred stock, par value (in dollars per share) | $ / shares			$ 0.0001			$ 0.0001			$ 0.0001		$ 0.0001
Preferred stock, authorized (in shares)			10,000,000			10,000,000			10,000,000		10,000,000
Common share, authorized (in shares)			500,000,000			500,000,000			500,000,000		500,000,000
Common share, issued (in shares)			97,890,705			97,890,705			97,890,705		56,455,376
Common share, outstanding (in shares)			97,890,705			97,890,705			97,890,705		54,655,376
Vesting of sponsor restricted shares (in shares)	1,800,000
Number of warrants outstanding			0	11,438,290		0			0
Number of securities called by warrants (in shares)			0			0			0		5,750,000
Exercise price of warrant (in dollars per share) | $ / shares				$ 11.50
Number of shares exercised				5,719,145
Proceeds from warrant exercises | $				$ 65,800,000
Warrants canceled (in shares)				61,710
Series A  preferred stock
Subsidiary or Equity Method Investee [Line Items]
Preferred stock, issued (in shares)			10,000			10,000			10,000		10,000
Preferred stock, outstanding (in shares)			10,000			10,000			10,000		10,000
Preferred stock, par value (in dollars per share) | $ / shares			$ 0.0001			$ 0.0001			$ 0.0001		$ 0.0001
Percentage of voting power of outstanding shares			25.00%			25.00%			25.00%
Liquidation amount per share (in dollars per share) | $ / shares			$ 0.01			$ 0.01			$ 0.01
Preferred stock, authorized (in shares)			10,000			10,000			10,000		10,000
Two Series A Preferred Stock | Minimum
Subsidiary or Equity Method Investee [Line Items]
Percentage of voting power of outstanding shares			25.00%			25.00%			25.00%
Roivant Sciences Ltd. (RSL) | Series A  preferred stock
Subsidiary or Equity Method Investee [Line Items]
Preferred stock, issued (in shares)			10,000			10,000			10,000
Preferred stock, outstanding (in shares)			10,000			10,000			10,000
Preferred stock, par value (in dollars per share) | $ / shares			$ 0.0001			$ 0.0001			$ 0.0001
Underwritten Public Offering
Subsidiary or Equity Method Investee [Line Items]
Number of shares issued in transaction			6,060,606		9,613,365
Common stock, sale price (in dollars per share) | $ / shares			$ 33.00		$ 14.50	$ 33.00			$ 33.00
Proceeds from issuance of common stock | $			$ 188,100,000		$ 131,000,000.0				$ 319,783,000	$ 0
Underwritten Public Offering | Roivant Sciences Ltd. (RSL)
Subsidiary or Equity Method Investee [Line Items]
Number of shares issued in transaction			380,000		1,034,483
Over-Allotment Option
Subsidiary or Equity Method Investee [Line Items]
Number of shares issued in transaction			790,513		1,253,917
IPO
Subsidiary or Equity Method Investee [Line Items]
Common stock, sale price (in dollars per share) | $ / shares		$ 16.50
Number of warrants outstanding												11,500,000
Exercise price of warrant (in dollars per share) | $ / shares												$ 11.50
Redemption price per warrant (in dollars per share) | $ / shares				$ 0.01
Required number of trading days | tradingDay		20
Consecutive number of trading days | tradingDay		30
Series A  preferred stock
Subsidiary or Equity Method Investee [Line Items]
Preferred stock, authorized (in shares)			10,010,000			10,010,000			10,010,000
Common stock
Subsidiary or Equity Method Investee [Line Items]
Common share, authorized (in shares)			500,000,000			500,000,000			500,000,000
Common stock, par value (in dollars per share) | $ / shares			$ 0.0001			$ 0.0001			$ 0.0001
Common share, issued (in shares)			56,455,376			56,455,376			56,455,376
Common share, outstanding (in shares)			54,655,376			54,655,376			54,655,376
Vesting of sponsor restricted shares (in shares)						900,000	900,000
Common stock | Roivant Sciences Ltd. (RSL)
Subsidiary or Equity Method Investee [Line Items]
Earnout shares for issuance (in shares) | $			$ 17,547,938			$ 17,547,938			$ 17,547,938
Common stock | Immunovant Sciences Ltd
Subsidiary or Equity Method Investee [Line Items]
Earnout shares for issuance (in shares) | $			$ 20,000,000			$ 20,000,000			$ 20,000,000
Warrant | IPO
Subsidiary or Equity Method Investee [Line Items]
Number of securities called by each warrant (in shares)												0.5
Number of securities called by warrants (in shares)												5,750,000

[1] Retroactively restated for reverse recapitalization as described in Note 1.