Fair Value of Financial Assets and Liabilities - Summary of Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Oct. 31, 2017	Apr. 30, 2017
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	$ 51,988	$ 52,494
Demand deposit accounts
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	50,211	46,164
Money market funds
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	178	3,532
Commercial paper
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	1,399	2,798
US government agencies debt securities
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	$ 200	$ 0