Commitments and Contingencies (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended	12 Months Ended
	Oct. 31, 2021	Oct. 31, 2020	Oct. 31, 2021	Apr. 30, 2021
Long-term Purchase Commitment [Line Items]
Royalty expense	$ 50	$ 12	$ 194	$ 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			12.50%