Summary of Significant Accounting Policies - Consolidated Financial Statements (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Jan. 31, 2021	Jan. 31, 2021	Apr. 30, 2021	Apr. 30, 2020	Apr. 30, 2019
Property, Plant and Equipment [Line Items]
Accrued liabilities	$ 2,207	$ 2,207	$ 2,231	$ 2,721
Total current liabilities	11,195	11,195	11,199	12,304
Total liabilities	17,174	17,174	20,163	15,652
Accumulated deficit	(71,638)	(71,638)	(72,530)	(72,892)
Total stockholders' equity	8,086	8,086	7,428	5,099	$ 2,137
Cost of oncology services	4,623	15,603	21,446	17,000
Total costs and operating expenses	9,830	29,462	40,674	34,044
Income (loss) from operations	982	1,014	366	(1,921)
Net income (loss)	$ 959	$ 1,035	$ 362	$ (2,093)
Basic net income (loss) per share (in usd per share)	$ 0.07	$ 0.08	$ 0.03	$ (0.18)
Diluted net income (loss) per share (in usd per share)	$ 0.07	$ 0.07	$ 0.02	$ (0.18)
Previously Reported
Property, Plant and Equipment [Line Items]
Accrued liabilities	$ 2,426	$ 2,426		$ 2,502
Total current liabilities	11,414	11,414		12,085
Total liabilities	17,393	17,393		15,433
Accumulated deficit	(71,857)	(71,857)		(72,673)
Total stockholders' equity	7,867	7,867		5,318	2,238
Cost of oncology services	4,842	15,822		16,882
Total costs and operating expenses	10,049	29,681		33,926
Income (loss) from operations	763	795		(1,803)
Net income (loss)	$ 740	$ 816		$ (1,975)
Basic net income (loss) per share (in usd per share)	$ 0.06	$ 0.06		$ (0.17)
Diluted net income (loss) per share (in usd per share)	$ 0.05	$ 0.06		$ (0.17)
Revision of Prior Period, Adjustment
Property, Plant and Equipment [Line Items]
Accrued liabilities	$ (219)	$ (219)		$ 219
Total current liabilities	(219)	(219)		219
Total liabilities	(219)	(219)		219
Accumulated deficit	219	219		(219)
Total stockholders' equity	219	219		(219)	$ (101)
Cost of oncology services	(219)	(219)		118
Total costs and operating expenses	(219)	(219)		118
Income (loss) from operations	219	219		(118)
Net income (loss)	$ 219	$ 219		$ (118)
Basic net income (loss) per share (in usd per share)	$ 0.01	$ 0.02		$ (0.01)
Diluted net income (loss) per share (in usd per share)	$ 0.02	$ 0.01		$ (0.01)