Presentation and Summary of Significant Accounting Policies - Diluted Earnings per Share for Class B Common Shares Using Two-Class Method (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended																12 Months Ended
		Apr. 30, 2018	[2]	Jan. 31, 2018	[2]	Oct. 31, 2017	[2]	Jul. 31, 2017	[2]	Apr. 30, 2017	[2]	Jan. 31, 2017	[2]	Oct. 31, 2016	[2]	Jul. 31, 2016	[2]	Apr. 30, 2018		Apr. 30, 2017		Apr. 30, 2016
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Basic weighted average common shares outstanding																		30,080		29,232		28,727
Weighted Average Number of Shares Outstanding, Diluted																		30,472		29,567		29,005
Basic, EPS	[1]																	$ 0.40		$ 0.50		$ 0.36
Diluted, EPS		$ 0.04		$ 0.18		$ 0.08		$ 0.09		$ 0.34		$ 0.08		$ 0.01		$ 0.06		$ 0.40	[1],[2]	$ 0.49	[1],[2]	$ 0.35	[1]
Class B Common Shares
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Undistributed and distributed earnings, Per basic																		$ 883		$ 1,208		$ 911
Reallocation of undistributed earnings from Class A Common shares to Class B Common shares																				(2)		2
Net earnings																		$ 883		$ 1,206		$ 913
Basic weighted average common shares outstanding																		2,275		2,439		2,584
Weighted Average Number of Shares Outstanding, Diluted																		2,275		2,439		2,584
Basic, EPS	[3]																	$ 0.39		$ 0.50		$ 0.35
Diluted, EPS	[3]																	$ 0.39		$ 0.49		$ 0.35

[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 $0.39, $0.49 and $0.35 for the years ended April 30, 2018, 2017 and 2016, respectively. See Note 1 to the Consolidated Financial Statements.

[2] Table may contain rounding

[3] Amounts adjusted for rounding