Presentation and Summary of Significant Accounting Policies - Diluted Earnings per Share for Class A Common Shares Using If-Converted 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
Class A common shares. 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 A Common Shares
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Undistributed and distributed earnings, Per basic										$ 6,355	$ 6,396	$ 11,170
Undistributed and distributed earnings, Class B conversion										387	407	883
Net earnings										$ 6,742	$ 6,803	$ 12,053
Basic weighted average common shares outstanding (in shares)										29,925	29,106	27,805
Common stock equivalents (in shares)										620	429	392
Weighted average number of shares including common stock equivalents, diluted										30,545	29,535	28,197
Class B conversion (in shares)										1,822	1,844	2,275
Class A common shares. diluted (in shares)										32,367	31,379	30,472
Basic, EPS (in usd per share)										$ 0.21	$ 0.22	$ 0.40
Diluted, EPS (in usd per share)	[1]									$ 0.21	$ 0.22	$ 0.40

[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.