Revenue from Contracts with Customers - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2021	Apr. 30, 2020
Disaggregation of Revenue [Line Items]
Total oncology services revenue	$ 41,040	$ 32,123
Pharmacology services
Disaggregation of Revenue [Line Items]
Total oncology services revenue	39,473	31,262
Personalized oncology services
Disaggregation of Revenue [Line Items]
Total oncology services revenue	166	790
Other TOS revenue
Disaggregation of Revenue [Line Items]
Total oncology services revenue	$ 1,401	$ 71