Presentation and Summary of Significant Accounting Policies - Basic Earnings per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		12 Months Ended
		Apr. 30, 2020	Apr. 30, 2019	Apr. 30, 2018
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Total (in usd per share)	[1]	$ 0.21	$ 0.22	$ 0.40
Basic weighted average common shares (in shares)		31,747	30,950	30,080
Class A Common Shares
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Distributed earnings per share (in usd per share)		$ 0.44	$ 0.44	$ 0.44
Undistributed earnings/(loss) per share (in usd per share)		(0.23)	(0.22)	(0.04)
Total (in usd per share)		$ 0.21	$ 0.22	$ 0.40
Distributed earnings		$ 13,219	$ 12,837	$ 12,321
Undistributed earnings/(loss)		(6,864)	(6,441)	(1,151)
Total		$ 6,355	$ 6,396	$ 11,170
Basic weighted average common shares (in shares)		29,925	29,106	27,805
Class B Common Shares
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Distributed earnings per share (in usd per share)		$ 0.44	$ 0.44	$ 0.43
Undistributed earnings/(loss) per share (in usd per share)		(0.23)	(0.22)	(0.04)
Total (in usd per share)		$ 0.21	$ 0.22	$ 0.39
Distributed earnings		$ 805	$ 819	$ 974
Undistributed earnings/(loss)		(418)	(412)	(91)
Total		$ 387	$ 407	$ 883
Basic weighted average common shares (in shares)		1,822	1,844	2,275

[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.