Fair Value of Financial Assets and Liabilities - Summary of Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Jul. 31, 2017	Apr. 30, 2017
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	$ 47,016	$ 52,494
Demand deposit accounts
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	39,509	46,164
Money market funds
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	3,660	3,532
Commercial paper
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	$ 3,847	$ 2,798