Presentation and Summary of Significant Accounting Policies - Diluted Earnings per Share for Class B Common Shares Using Two-Class Method (Details) - USD ($) $ / shares in Units, shares in Thousands, $ 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
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Basic weighted average common shares outstanding (in shares)										31,747	30,950	30,080
Diluted (in shares)										32,367	31,378	30,472
Basic, EPS (in usd per share)	[1]									$ 0.21	$ 0.22	$ 0.40
Diluted, EPS (in usd per share)		$ 0.02	$ 0.10	$ 0.05	$ 0.04	$ 0.06	$ 0.07	$ 0.04	$ 0.04	$ 0.21	$ 0.22	$ 0.40
Class B Common Shares
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Undistributed and distributed earnings, Per basic										$ 387	$ 407	$ 883
Reallocation of undistributed earnings from Class A Common Shares to Class B Common Shares										5	2	0
Net earnings										$ 392	$ 409	$ 883
Basic weighted average common shares outstanding (in shares)										1,822	1,844	2,275
Diluted (in shares)										1,822	1,844	2,275
Basic, EPS (in usd per share)										$ 0.21	$ 0.22	$ 0.39
Diluted, EPS (in usd per share)										$ 0.22	$ 0.22	$ 0.39

[1] Diluted per share amounts for Class A shares are shown above. Diluted per share for Class B shares under the two-class method are $0.22, $0.22 and $0.39 for the years ended April 30, 2020, 2019 and 2018, respectively. See Note 1 to the Consolidated Financial Statements.