Financial Statements and Supplementary Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Apr. 30, 2020	Jan. 31, 2020	Oct. 31, 2019	Jul. 31, 2019	Apr. 30, 2019	Jan. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Apr. 30, 2020	Apr. 30, 2019	Apr. 30, 2018
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 29,273	$ 30,600	$ 28,210	$ 27,383	$ 26,271	$ 27,003	$ 28,033	$ 27,399	$ 115,466	$ 108,706	$ 112,703
Gross margin	15,908	17,442	15,186	14,622	14,282	14,039	14,667	13,752	63,158	56,740	62,703
Operating income	1,589	2,819	843	797	1,013	2,130	1,526	607	6,048	5,276	13,531
Net earnings	$ 545	$ 3,286	$ 1,759	$ 1,152	$ 1,874	$ 2,301	$ 1,243	$ 1,385	$ 6,742	$ 6,803	$ 12,053
Diluted earnings per share	$ 0.02	$ 0.10	$ 0.05	$ 0.04	$ 0.06	$ 0.07	$ 0.04	$ 0.04	$ 0.21	$ 0.22	$ 0.40