CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities:
Net loss	$ (52,625)	$ (30,834)	$ (19,702)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	7,741	2,730	812
Depreciation and amortization	533	148	109
Change in fair value of warrant liability		5,452	972
Stock options in exchange for consulting services			26
Net amortization (accretion) of premium and discount on short-term investments	(945)	(1,715)	(123)
Noncash rent expense		93
Noncash interest expense	156
Changes in operating assets and liabilities:
Research and development incentives receivable	(628)	(255)	(767)
Prepaid expenses and other current assets	933	(801)	(305)
Operating lease, right-of-use-asset	588
Finance lease, right-of-use-asset	1,274
Long term prepaid rent	(15,787)
Accounts payable	(3,821)	120	1,596
Accrued expenses and other current liabilities	2,479	(292)	1,393
Operating lease liabilities	(450)
Deferred rent		(24)	(25)
Net cash used in operating activities	(60,552)	(25,378)	(16,014)
Cash flows from investing activities:
Purchases of property, plant and equipment	(6,540)	(2,600)	(136)
Purchase of short-term investments	(149,682)	(189,931)	(52,463)
Proceed from sales and maturities of short-term investments	150,989	126,587	8,553
Net cash provided by (used in) investing activities	(5,233)	(65,944)	(44,046)
Cash flows from financing activities:
Proceeds from issuance of series B convertible preferred stock, net of issuance costs			54,752
Proceeds from issuance of common stock in initial public offering, net of underwriting fees and discounts		103,341
Proceeds from issuance of common stock in follow-on public offering, net of underwriting fees and discounts	57,453
Proceeds from issuance of prefunded warrants to purchase common stock, net of underwriting fees and discounts	28,145
Proceeds from issuance of common stock through ATM sales	4,431
Proceeds from long-term debt	10,000
Exercise of stock options	551	206
Payment of issuance costs	(355)	(2,157)
Principal payment of finance lease obligation	(59)
Net cash provided by financing activities	100,166	101,390	54,752
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(135)	(839)	2,297
Net increase (decrease) in cash, cash equivalents and restricted cash	34,246	9,229	(3,011)
Cash, cash equivalents and restricted cash at beginning of year	26,890	17,661	20,672
Cash, cash equivalents and restricted cash at end of year	61,136	26,890	17,661
Supplemental disclosure of cash flow information
Cash paid for interest	578
Supplemental disclosure of non-cash investing and financing activities:
Net unrealized gain (loss) on short-term investments	309	80	$ (65)
Purchases of property and equipment included in accounts payable	209	5,047
Conversion of convertible preferred stock into common stock		7,094
Conversion of convertible preferred stock warrants into common stock warrants		86,361
Amounts capitalized under built-to-suit lease transaction		$ 4,292
Lease assets obtained in exchange for new financing lease liabilities	48,224
Lease assets obtained in exchange for new operating lease liabilities	5,152
Adjustment for non-cash lease termination	$ 117