Fair Value of Financial Assets and Liabilities - Summary of Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Jan. 31, 2017	Apr. 30, 2016
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	$ 38,287	$ 43,963
Demand deposit accounts
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	37,025	38,692
Money market funds
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	587	922
Commercial paper
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	$ 675	$ 4,349