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, 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
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Basic weighted average common shares outstanding (in shares)										30,950	30,080	29,232
Class A common shares. diluted (in shares)										31,378	30,472	29,567
Basic, EPS (in usd per share)	[1]									$ 0.22	$ 0.40	$ 0.50
Diluted, EPS (in usd per share)		$ 0.06	$ 0.07	$ 0.04	$ 0.04	$ 0.04	$ 0.18	$ 0.08	$ 0.09	$ 0.22	$ 0.40	$ 0.49
Class A Common Shares
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Undistributed and distributed earnings, Per basic										$ 6,396	$ 11,170	$ 13,413
Undistributed and distributed earnings, Class B conversion										407	883	1,208
Net earnings										$ 6,803	$ 12,053	$ 14,621
Basic weighted average common shares outstanding (in shares)										29,106	27,805	26,793
Common stock equivalents (in shares)										429	392	335
Weighted average number of shares including common stock equivalents, diluted										29,535	28,197	27,128
Class B conversion (in shares)										1,844	2,275	2,439
Class A common shares. diluted (in shares)										31,379	30,472	29,567
Basic, EPS (in usd per share)										$ 0.22	$ 0.40	$ 0.50
Diluted, EPS (in usd per share)	[1]									$ 0.22	$ 0.40	$ 0.49

[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, $0.39 and $0.49 for the years ended April 30, 2019, 2018 and 2017, respectively. See Note 1 to the Consolidated Financial Statements.