Consolidated Statements of Operations and Comprehensive Loss - USD ($)	12 Months Ended
	Apr. 30, 2022	Apr. 30, 2021	Apr. 30, 2020
Income Statement [Abstract]
Revenue			$ 12,690,000
Operating expenses:
Research and development	$ 70,167,000	$ 41,286,000	40,194,000
General and administrative	26,446,000	16,637,000	13,029,000
Total operating expenses	96,613,000	57,923,000	53,223,000
Operating loss	(96,613,000)	(57,923,000)	(40,533,000)
Other income:
Interest income	1,090,000	903,000	1,830,000
Foreign currency exchange gain (loss)	(1,537,000)	847,000	(367,000)
Other income	14,721,000	9,929,000	9,830,000
Total other income	14,274,000	11,679,000	11,293,000
Loss before income taxes	(82,339,000)	(46,244,000)	(29,240,000)
Income tax (benefit) expense	0	0	(124,000)
Net loss	(82,339,000)	(46,244,000)	(29,116,000)
Other comprehensive income (loss):
Foreign currency translation (loss) gain	(1,499,000)	1,076,000	59,000
Unrealized holding (loss) gain on available-for-sale securities	(1,511,000)	(473,000)	285,000
Reclassification adjustment for realized loss (gain) on available for sale securities included in net loss	581,000	(153,000)	(300,000)
Total other comprehensive (loss) income:	(2,429,000)	450,000	44,000
Comprehensive loss	$ (84,768,000)	$ (45,794,000)	$ (29,072,000)
Net loss per share, basic	$ (3.36)	$ (2.42)	$ (1.64)
Net loss per share, diluted	$ (3.36)	$ (2.42)	$ (1.64)
Weighted average common shares outstanding, basic	24,473,092	19,094,440	17,748,666
Weighted average common shares outstanding, diluted	24,473,092	19,094,440	17,748,666