Related Party Transactions (Details) - USD ($) $ / shares in Units, $ in Millions				1 Months Ended		12 Months Ended
	Dec. 18, 2018	Jul. 09, 2018	Jun. 05, 2018	Feb. 29, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
RSI
Related Party Transaction [Line Items]
Expense under service agreement						$ 0.1	$ 5.1
Private Placement | Roivant Sciences, Ltd.
Related Party Transaction [Line Items]
Net proceeds from common stock issued		$ 25.0
Number of shares issued and sold (in shares)			1,785,714
Price of shares issued and sold (in dollars per share)			$ 14
Public Offering
Related Party Transaction [Line Items]
Net proceeds from common stock issued	$ 31.6			$ 70.8	$ 37.9
Number of shares issued and sold (in shares)	4,145,115			16,631,336	3,333,333
Price of shares issued and sold (in dollars per share)	$ 8				$ 12	$ 3.75	$ 12
Gross proceeds from common stock issued	$ 33.2				$ 40.0
Warrants issued (in dollars per share)				$ 3.74999
Warrants issued (in shares)				3,301,998
Public Offering | Roivant Sciences, Ltd.
Related Party Transaction [Line Items]
Number of shares issued and sold (in shares)	1,250,000			5,333,333	833,333
Underwriter's Option
Related Party Transaction [Line Items]
Number of shares issued and sold (in shares)	395,115			2,600,000