Revenue from Contracts with Customers (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Oct. 31, 2020	Oct. 31, 2019	Oct. 31, 2020	Oct. 31, 2019
Disaggregation of Revenue [Line Items]
Description of timing			The majority of the Company's revenue arrangements are service contracts that are complete within a year or less. There are a few contracts that range in duration between 1 and 3 years.
Oncology services revenue	$ 10,117	$ 7,625	$ 19,664	$ 14,362
Pharmacology services
Disaggregation of Revenue [Line Items]
Oncology services revenue	10,041	7,358	19,454	13,888
Personalized oncology services
Disaggregation of Revenue [Line Items]
Oncology services revenue	37	232	150	412
Other
Disaggregation of Revenue [Line Items]
Oncology services revenue	$ 39	$ 35	$ 60	$ 62