Revenue Recognition - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2017	Jan. 31, 2016	Apr. 30, 2016
Revenue Recognition [Line Items]
Amounts received for reimbursement of travel and other out-of-pocket expenses	$ 414,000	$ 555,000	$ 1,600,000	$ 1,800,000
Unbilled amounts	2,415,000		2,415,000		$ 3,444,000
Unbilled License Fees
Revenue Recognition [Line Items]
Unbilled amounts	126,000		126,000		1,600,000
Unbilled Services Revenues
Revenue Recognition [Line Items]
Unbilled amounts	$ 2,300,000		$ 2,300,000		$ 1,900,000
Minimum
Revenue Recognition [Line Items]
Contractual period of maintenance contract			1 year
Maximum
Revenue Recognition [Line Items]
Contractual period of maintenance contract			3 years