Condensed Consolidated Statement of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Shares	Common Shares Subscribed	Additional Paid in Capital	Accumulated Other Comprehensive Income	Accumulated Deficit	Public Offering	Public Offering Common Shares	Public Offering Additional Paid in Capital	Cowen and Company, LLC Private Placement	Cowen and Company, LLC Private Placement Common Shares	Cowen and Company, LLC Private Placement Additional Paid in Capital	Roivant Sciences, Ltd. Private Placement	Roivant Sciences, Ltd. Private Placement Common Shares	Roivant Sciences, Ltd. Private Placement Additional Paid in Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adjustment to adopt ASU 2016-09				$ 122		$ (122)
Beginning balance (in shares) at Mar. 31, 2017		60,275,757
Beginning balance at Mar. 31, 2017	$ 166,776	$ 1	$ (1)	251,733	$ 140	(85,097)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued to settle the warrant liability to Takeda (in shares)		4,432
Shares issued to settle the warrant liability to Takeda	58	$ 0		58
Share-based compensation expense (in shares)		564,111
Share-based compensation expense	1,954	$ 0		1,954
Capital contribution — share-based compensation	247			247
Foreign currency translation adjustment	264				264
Net loss	(23,317)					(23,317)
Ending balance (in shares) at Jun. 30, 2017		60,844,300
Ending balance at Jun. 30, 2017	145,982	$ 1	(1)	254,114	404	(108,536)
Beginning balance (in shares) at Mar. 31, 2017		60,275,757
Beginning balance at Mar. 31, 2017	166,776	$ 1	(1)	251,733	140	(85,097)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(53,225)
Ending balance (in shares) at Sep. 30, 2017		60,849,236
Ending balance at Sep. 30, 2017	118,719	$ 1	(1)	256,875	288	(138,444)
Beginning balance (in shares) at Jun. 30, 2017		60,844,300
Beginning balance at Jun. 30, 2017	145,982	$ 1	(1)	254,114	404	(108,536)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation expense (in shares)		0
Share-based compensation expense	2,519	$ 0		2,519
Capital contribution — share-based compensation	230			230
Foreign currency translation adjustment	(116)				(116)
Issuance of common shares upon exercise of stock options (in shares)		4,936
Issuance of common shares upon exercise of stock options	12			12
Net loss	(29,908)					(29,908)
Ending balance (in shares) at Sep. 30, 2017		60,849,236
Ending balance at Sep. 30, 2017	$ 118,719	$ 1	$ (1)	256,875	288	(138,444)
Beginning balance (in shares) at Mar. 31, 2018	60,997,856	60,997,856
Beginning balance at Mar. 31, 2018	$ 37,729	$ 1		266,178	24	(228,474)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common shares (in shares)											2,767,129			1,110,015
Issuance of common shares										$ 57,315	$ 0	$ 57,315	$ 22,500	$ 0	$ 22,500
Share-based compensation expense (in shares)		0
Share-based compensation expense	4,053	$ 0		4,053
Capital contribution — share-based compensation	191			191
Foreign currency translation adjustment	425				425
Issuance of common shares upon exercise of stock options (in shares)		16,218
Issuance of common shares upon exercise of stock options	76			76
Net loss	(62,134)					(62,134)
Ending balance (in shares) at Jun. 30, 2018		64,891,218
Ending balance at Jun. 30, 2018	$ 60,155	$ 1		350,313	449	(290,608)
Beginning balance (in shares) at Mar. 31, 2018	60,997,856	60,997,856
Beginning balance at Mar. 31, 2018	$ 37,729	$ 1		266,178	24	(228,474)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common shares upon exercise of stock options (in shares)	73,989
Net loss	$ (127,904)
Ending balance (in shares) at Sep. 30, 2018	68,484,888	68,484,888
Ending balance at Sep. 30, 2018	$ 74,101	$ 1		430,101	377	(356,378)
Beginning balance (in shares) at Jun. 30, 2018		64,891,218
Beginning balance at Jun. 30, 2018	60,155	$ 1		350,313	449	(290,608)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common shares (in shares)								3,533,399
Issuance of common shares							$ 74,391	$ 0	$ 74,391
Share-based compensation expense (in shares)		0
Share-based compensation expense	4,529	$ 0		4,529
Capital contribution — share-based compensation	196			196
Capital contribution from RSI and RSG	212			212
Foreign currency translation adjustment	(72)				(72)
Issuance of common shares upon exercise of stock options and vesting of RSUs (in shares)		60,271
Issuance of common shares upon exercise of stock options and vesting of RSUs	460			460
Net loss	$ (65,770)					(65,770)
Ending balance (in shares) at Sep. 30, 2018	68,484,888	68,484,888
Ending balance at Sep. 30, 2018	$ 74,101	$ 1		$ 430,101	$ 377	$ (356,378)