Consolidated Valuation Accounts (Detail) - Allowance for Doubtful Accounts - USD ($) $ in Thousands		12 Months Ended
		Apr. 30, 2015	Apr. 30, 2014	Apr. 30, 2013
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of year		$ 222	$ 337	$ 171
Amounts charged to expense		178	(56)	216
Other Additions	[1]	1	86	0
Deductions	[2]	186	145	50
Balance at end of year		$ 215	$ 222	$ 337

[1] Recovery of previously written-off amounts.

[2] Write-off of uncollectible accounts.