Condensed Consolidated Statements of Operations - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Income Statement [Abstract]
Collaboration revenue		$ 1,379	$ 0	$ 1,379	$ 0
License and milestone revenue		0	0	33,333	0
Total revenues		1,379	0	34,712	0
Operating expenses:
Research and development		30,453	48,927	115,160	150,847
Selling, general and administrative		49,243	29,142	103,387	59,897
Total operating expenses		79,696	78,069	218,547	210,744
Loss from operations		(78,317)	(78,069)	(183,835)	(210,744)
Interest expense	[1]	2,609	3,657	6,908	11,238
Loss on extinguishment of debt		0	4,851	0	4,851
Interest income		(32)	(597)	(178)	(2,305)
Other income, net		(5,891)	(567)	(16,178)	(1,151)
Loss before income taxes		(75,003)	(85,413)	(174,387)	(223,377)
Income tax (benefit) expense		(1,154)	191	(616)	699
Net loss		$ (73,849)	$ (85,604)	$ (173,771)	$ (224,076)
Net loss per common share — basic and diluted (in USD per share)		$ (0.82)	$ (0.96)	$ (1.94)	$ (2.64)
Weighted average common shares outstanding — basic and diluted (in shares)		90,096,557	88,893,579	89,715,160	84,750,114
Revenue, Product and Service [Extensible List]		us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Selling, general and administrative		$ 49,243	$ 29,142	$ 103,387	$ 59,897
Interest expense	[1]	2,609	3,657	6,908	11,238
Sumitomo Dainippon Pharma, Co., Ltd. and Sunovion Pharmaceuticals Inc. | Majority Shareholder
Operating expenses:
Selling, general and administrative		1,671		3,076
Selling, general and administrative		1,671		3,076
Sumitomo Dainippon Pharma Co., Ltd. | Majority Shareholder | Term Loan | Letter Agreement with Sumitomo Dainippon Pharma, Co., Ltd.
Operating expenses:
Interest expense		2,569	16	6,868	16
Interest expense		$ 2,569	$ 16	$ 6,868	$ 16

[1] Includes $2,569 and $6,868 of interest expense from related-party long-term debt with Sumitomo Dainippon Pharma for the three and nine months ended December 31, 2020, respectively, and $16 for both the three and nine months ended December 31, 2019. (see Note 5(A)).