Earnings Per Common Share - 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
		Jul. 31, 2019	Jul. 31, 2018
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Basic shares used in calculation of earnings per common share (in shares)		31,270	30,725
Diluted, Class A Common Shares (in shares)		31,951	31,343
Basic EPS (in usd per share)	[1]	$ 0.04	$ 0.05
Diluted EPS (in usd per share)	[1]	$ 0.04	$ 0.04
Class A Common Shares
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Undistributed & distributed earnings		$ 1,082	$ 1,299
Undistributed & distributed earnings, class B conversion (in usd per share)		70	86
Net earnings		$ 1,152	$ 1,385
Basic shares used in calculation of earnings per common share (in shares)		29,448	28,814
Common Stock Equivalents (in shares)		681	618
Weighted Average Number of Shares Including Common Stock Equivalents, Diluted (in shares)		30,129	29,432
Class B Conversion (in shares)		1,822	1,911
Diluted, Class A Common Shares (in shares)		31,951	31,343
Basic EPS (in usd per share)		$ 0.04	$ 0.05
Diluted EPS (in usd per share)		$ 0.04	$ 0.04

[1] (a)Basic per share amounts are the same for Class A and Class B shares. Diluted per share amounts for Class A shares are shown above. Diluted earnings per share for Class B shares under the two-class method are $0.04 and $0.05 for the three months ended July 31, 2019 and 2018, respectively. See Note E to the Condensed Consolidated Financial Statements.