Significant Accounting Policies - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Oct. 31, 2021	Jul. 31, 2021	Oct. 31, 2020	Jul. 31, 2020	Oct. 31, 2021	Oct. 31, 2020	Apr. 30, 2021
Accounting Policies [Abstract]
Cash equivalents	$ 0				$ 0		$ 0
Net income	277	$ (172)	$ 1	$ 75	105	$ 76
Net cash provided by (used in) operating activities					1,444	164
Accumulated deficit	72,425				72,425		72,530
Working capital	1,200				1,200
Cash and cash equivalents	4,781				4,781		4,687
Unrecognized tax benefits	181				181		181
Accrued income tax penalties and interest	3				3		$ 3
Income tax penalties and interest expense	0		0		0	0
Unrecognized tax benefits anticipated during the next 12 months	0				0
Provision for income taxes	$ 12		$ 15		$ 26	$ 28