Fair Value of Financial Assets and Liabilities - Summary of Short-Term Investments (Detail) - USD ($) $ in Thousands	Apr. 30, 2015	Apr. 30, 2014
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 52,758	$ 40,692
Gross Unrealized Gains	30	19
Gross Unrealized Losses	(58)	(11)
Fair Value	52,730	40,700
Certificates of Deposit
Schedule of Available-for-sale Securities [Line Items]
Cost	4,000	7,466
Gross Unrealized Gains	4	17
Gross Unrealized Losses		(9)
Fair Value	4,004	7,474
Municipal Bonds
Schedule of Available-for-sale Securities [Line Items]
Cost	4,564
Gross Unrealized Gains	17
Gross Unrealized Losses	(16)
Fair Value	4,565
Commercial Paper
Schedule of Available-for-sale Securities [Line Items]
Cost	6,269
Gross Unrealized Gains	4
Fair Value	6,273
US Treasury notes
Schedule of Available-for-sale Securities [Line Items]
Cost	23,820	33,226
Gross Unrealized Gains	1	2
Gross Unrealized Losses	(12)	(2)
Fair Value	23,809	$ 33,226
U.S. Treasury Bonds
Schedule of Available-for-sale Securities [Line Items]
Cost	5,001
Gross Unrealized Losses	(2)
Fair Value	4,999
Corporate Notes
Schedule of Available-for-sale Securities [Line Items]
Cost	2,709
Gross Unrealized Gains	1
Gross Unrealized Losses	(2)
Fair Value	2,708
Corporate Bonds
Schedule of Available-for-sale Securities [Line Items]
Cost	6,395
Gross Unrealized Gains	3
Gross Unrealized Losses	(26)
Fair Value	$ 6,372

This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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-SubTopic 10

-Section 50

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

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-Name Accounting Standards Codification

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