Amortized Cost and Fair Values of Marketable Securities Classified as Available-For-Sale Investments (Detail) - USD ($) $ in Thousands		Apr. 30, 2016	Apr. 30, 2015
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value		$ 0	$ 13,177	[1]
Corporate Bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost			13,167
Gross Unrealized Gains			11
Gross Unrealized Losses	[2]		(1)
Estimated Fair Value	[1]		$ 13,177

[1] The Company's financial assets measured at fair value on a recurring basis include trading securities classified as Level 1 and available-for-sale securities classified as Level 2. As of April 30, 2016 and 2015, the Company had no investments classified as Level 3.

[2] There are no marketable securities that have been in a continuous unrealized loss position for 12 months or more.