Consolidated Statements of Cash Flows - USD ($) $ in Thousands		12 Months Ended
		Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities:
Net loss		$ (255,134)	$ (288,989)	$ (273,551)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Share-based compensation		53,676	40,251	18,696
Depreciation and amortization	[1]	2,479	1,765	438
Non-cash interest expense	[2]	635	1,486	2,084
Loss on extinguishment of debt		0	4,851	0
Foreign currency transaction (gain) loss		(16,176)	(1,621)	309
Other		537	(359)	926
Changes in operating assets and liabilities:
Accounts receivable		(3,570)	0	0
Inventory		(2,611)	0	0
Prepaid expenses and other current assets		(5,267)	1,925	(5,055)
Income tax receivable		0	524	476
Other assets		(1,441)	(10)	76
Accounts payable		2,457	4,315	6,441
Interest payable		0	(1,077)	795
Accrued expenses and other current liabilities		15,552	(24,675)	21,510
Deferred revenue		457,933	40,000	0
Amount due to collaboration partner		1,954	0	0
Cost share advance from collaboration partner		121,227	0	0
Operating lease liabilities		(1,516)	(882)	0
Deferred rent		0	0	749
Deferred interest payable		0	(2,273)	2,018
Amounts due to related parties		528	15	0
Other liabilities		(635)	3,582	0
Net cash provided by (used in) operating activities		370,628	(221,172)	(224,088)
Cash flows from investing activities:
Purchases of marketable securities		(63,824)	(32,076)	0
Maturities of marketable securities		33,261	29,240	0
Sales of marketable securities		23,125	0	0
Purchases of property and equipment		(1,773)	(1,099)	(1,236)
Net cash used in investing activities		(9,211)	(3,935)	(1,236)
Cash flows from financing activities:
Cash proceeds from issuance of common shares		0	137,004	218,925
Proceeds from related party debt financing		245,000	113,700	0
Proceeds from stock option exercises		6,709	942	1,300
Proceeds from third-party debt financing, net of financing costs paid		0	0	53,974
Payment of tax withholding on net settlement of share awards		(13,664)	0	0
Payment of third-party debt financings and redemption and administration fees		0	(105,720)	(300)
Net cash provided by financing activities		238,045	145,926	273,899
Net change in cash, cash equivalents and restricted cash		599,462	(79,181)	48,575
Cash, cash equivalents and restricted cash, beginning of period		78,018	157,199	108,624
Cash, cash equivalents and restricted cash, end of period		677,480	78,018	157,199
Non-cash financing activities:
Reclassification of share-based compensation awards from additional paid-in capital to current liabilities		17,473	0	0
Change in fair value of share-based awards recorded to additional paid-in capital		10,609	0	0
Reclassification of share-based compensation liabilities to additional paid-in capital upon settlement of awards		6,446	0	0
Equipment purchases included in accounts payable		18	0	0
Supplemental disclosure of cash paid:
Income taxes		513	38	0
Interest		0	13,030	3,923
Interest (related party)		$ 9,819	$ 1,426	$ 0

[1] Includes amortization of operating lease right-of-use assets.

[2] Includes imputed interest on cost share advance from collaboration partner for the year ended March 31, 2021 and amortization of debt discount and issuance costs for the years ended March 31, 2020 and 2019.