Financial Statements and Supplementary Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Apr. 30, 2019	Jan. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Apr. 30, 2018	Jan. 31, 2018	Oct. 31, 2017	Jul. 31, 2017	Apr. 30, 2019	Apr. 30, 2018	Apr. 30, 2017
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 26,271	$ 27,003	$ 28,033	$ 27,399	$ 29,363	$ 30,117	$ 26,337	$ 26,886	$ 108,706	$ 112,703	$ 106,286
Gross margin	14,282	14,039	14,667	13,752	16,426	17,046	14,006	15,225	56,740	62,703	55,202
Operating income	1,013	2,130	1,526	607	2,463	4,204	3,242	3,622	5,276	13,531	7,766
Net earnings	$ 1,874	$ 2,301	$ 1,243	$ 1,385	$ 1,268	$ 5,580	$ 2,480	$ 2,725	$ 6,803	$ 12,053	$ 14,621
Diluted earnings per share	$ 0.06	$ 0.07	$ 0.04	$ 0.04	$ 0.04	$ 0.18	$ 0.08	$ 0.09	$ 0.22	$ 0.40	$ 0.49