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, 2019	Apr. 30, 2018	Apr. 30, 2017
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Total (in usd per share)	[1]	$ 0.22	$ 0.40	$ 0.50
Basic weighted average common shares (in shares)		30,950	30,080	29,232
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)		(0.22)	(0.04)	0.06
Total (in usd per share)		$ 0.22	$ 0.40	$ 0.50
Distributed earnings		$ 12,837	$ 12,321	$ 11,845
Undistributed earnings/(loss)		(6,441)	(1,151)	1,568
Total		$ 6,396	$ 11,170	$ 13,413
Basic weighted average common shares (in shares)		29,106	27,805	26,793
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	$ 0.43	$ 0.44
Undistributed earnings/(loss) per share (in usd per share)		(0.22)	(0.04)	0.06
Total (in usd per share)		$ 0.22	$ 0.39	$ 0.50
Distributed earnings		$ 819	$ 974	$ 1,066
Undistributed earnings/(loss)		(412)	(91)	142
Total		$ 407	$ 883	$ 1,208
Basic weighted average common shares (in shares)		1,844	2,275	2,439

[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.