Shareholders' Equity - Narrative (Details) - USD ($)		1 Months Ended				2 Months Ended	3 Months Ended	6 Months Ended	12 Months Ended
	Apr. 02, 2018	Aug. 31, 2018	Jul. 31, 2018	Apr. 30, 2018	Oct. 31, 2017	Aug. 31, 2018	Sep. 30, 2018	Sep. 30, 2018	Mar. 31, 2017
Subsidiary, Sale of Stock [Line Items]
Shares issued to settle the warrant liability to Takeda (in shares)									4,432
Private Placement
Subsidiary, Sale of Stock [Line Items]
Number of shares issued (in shares)					138,361
Net proceeds from sale of shares					$ 2,000,000
Public Offering
Subsidiary, Sale of Stock [Line Items]
Number of shares issued (in shares)			3,333,334
Price of shares (in USD per share)			$ 22.5
Net proceeds from sale of shares						$ 74,400,000
Underwriter's Over-Allotment Option
Subsidiary, Sale of Stock [Line Items]
Number of shares issued (in shares)		200,065
Price of shares (in USD per share)		$ 22.5				$ 22.5
Roivant Sciences, Ltd. | Private Placement
Subsidiary, Sale of Stock [Line Items]
Number of shares issued (in shares)	1,110,015
Price of shares (in USD per share)	$ 20.27
Gross proceeds from sale of shares				$ 22,500,000
Cowen and Company, LLC | Private Placement
Subsidiary, Sale of Stock [Line Items]
Number of shares issued (in shares)							0	2,767,129
Price of shares (in USD per share)							$ 21.47	$ 21.47
Net proceeds from sale of shares								$ 57,300,000
Aggregate offering price	$ 100,000,000
Remaining capacity in offering program							$ 40,600,000	$ 40,600,000