Earnings Per Common share - Basic Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		6 Months Ended
		Oct. 31, 2018	Oct. 31, 2017	Oct. 31, 2018	Oct. 31, 2017
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Total	[1]	$ 0.04	$ 0.08	$ 0.09	$ 0.17
Basic weighted average common shares outstanding		30,926	29,906	30,825	29,788
Class A Common Shares
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Distributed earnings		$ 0.11	$ 0.11	$ 0.22	$ 0.22
Undistributed losses		(0.07)	(0.03)	(0.13)	(0.05)
Total	[2]	$ 0.04	$ 0.08	$ 0.09	$ 0.17
Distributed earnings		$ 3,200	$ 3,064	$ 6,396	$ 6,078
Undistributed losses		(2,033)	(768)	(3,927)	(1,269)
Total		$ 1,167	$ 2,296	$ 2,469	$ 4,809
Basic weighted average common shares outstanding		29,104	27,589	28,959	27,448
Class B Common Shares
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Distributed earnings		$ 0.11	$ 0.11	$ 0.22	$ 0.22
Undistributed losses		(0.07)	(0.03)	(0.13)	(0.05)
Total	[2]	$ 0.04	$ 0.08	$ 0.09	$ 0.17
Distributed earnings		$ 205	$ 249	$ 409	$ 505
Undistributed losses		(129)	(65)	(250)	(109)
Total		$ 76	$ 184	$ 159	$ 396
Basic weighted average common shares outstanding		1,822	2,317	1,866	2,340

[1] 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 $0.08 for the three months ended October 31, 2018 and 2017, and $0.09 and $0.17 for the six months ended October 31, 2018 and 2017, respectively. See Note D to the Condensed Consolidated Financial Statements.

[2] Amounts adjusted for rounding