Consolidated Valuation Accounts (Detail) - Allowance for Doubtful Accounts - USD ($) $ in Thousands		12 Months Ended
		Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2016
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of year		$ 171	$ 178	$ 215
Amounts charged to expense		24	39
Other Additions	[1]			41
Deductions	[2]	36	46	78
Balance at end of year		$ 159	$ 171	$ 178

[1] Recovery of previously written-off amounts.

[2] Write-off of uncollectible accounts.