Significant Accounting Policies - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Jan. 31, 2022	Oct. 31, 2021	Jul. 31, 2021	Jan. 31, 2021	Oct. 31, 2020	Jul. 31, 2020	Jan. 31, 2022	Jan. 31, 2021	Apr. 30, 2021
Accounting Policies [Abstract]
Cash equivalents	$ 0						$ 0		$ 0
Net income	787	$ 277	$ (172)	$ 959	$ 1	$ 75	892	$ 1,035
Net cash provided by (used in) operating activities							5,701	299
Accumulated deficit	71,638						71,638		72,530
Working capital	2,300						2,300
Cash and cash equivalents	8,701						8,701		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	$ 11			$ 15			$ 37	$ 43