Consolidated Valuation Accounts (Detail) - Allowance for Doubtful Accounts - USD ($) $ in Thousands		12 Months Ended
		Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of year		$ 178	$ 215	$ 222
Amounts charged to expense		39		178
Other Additions	[1]		41	1
Deductions	[2]	46	78	186
Balance at end of year		$ 171	$ 178	$ 215

[1] Recovery of previously written-off amounts.

[2] Write-off of uncollectible accounts.