Shareholders' Equity - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended		3 Months Ended		9 Months Ended
	Jun. 04, 2019	Apr. 30, 2018	Oct. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Public Offering
Subsidiary, Sale of Stock [Line Items]
Number of shares issued (in shares)	17,424,243
Price of shares (in USD per share)	$ 8.25
Net proceeds from sale of shares	$ 134.5
Underwriter's Over-Allotment Option
Subsidiary, Sale of Stock [Line Items]
Number of shares issued (in shares)	2,272,727
Private Placement
Subsidiary, Sale of Stock [Line Items]
Number of shares issued (in shares)			138,361
Net proceeds from sale of shares			$ 2.0
Cowen and Company, LLC | Private Placement
Subsidiary, Sale of Stock [Line Items]
Number of shares issued (in shares)				0	0	106,494	2,767,129
Price of shares (in USD per share)				$ 24.65	$ 21.47	$ 24.65	$ 21.47
Net proceeds from sale of shares				$ 2.5	$ 57.3
Aggregate offering price		$ 100.0
Remaining capacity in offering program				$ 10.4		$ 10.4
Majority Shareholder | Public Offering
Subsidiary, Sale of Stock [Line Items]
Number of shares issued (in shares)	2,424,242
Net proceeds from sale of shares	$ 20.0
Majority Shareholder | 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
Net proceeds from sale of shares		$ 22.5