Commitments and Contingencies (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended	12 Months Ended
	Jan. 31, 2022	Jan. 31, 2021	Jan. 31, 2022	Apr. 30, 2021
Long-term Purchase Commitment [Line Items]
Royalty expense	$ 87	$ 32	$ 286	$ 127
Minimum
Long-term Purchase Commitment [Line Items]
Royalty fee per tumor sample			$ 0
Royalty payment, as percent of contract price			2.00%
Maximum
Long-term Purchase Commitment [Line Items]
Royalty fee per tumor sample			$ 10
Royalty payment, as percent of contract price			20.00%