Fair Value of Financial Assets and Liabilities - Summary of Cash and Cash Equivalents (Detail) - USD ($) $ in Thousands	Apr. 30, 2015	Apr. 30, 2014
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	$ 54,041	$ 31,934
Demand deposits accounts
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	49,977	24,721
Money Market Funds
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	2,831	6,971
Certificates of Deposit
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents		$ 242
Municipal Bonds
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	102
Commercial Paper
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	875
Corporate Bonds
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	$ 256