Revenue Recognition - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Jan. 31, 2014	Jan. 31, 2013	Jan. 31, 2014	Jan. 31, 2013	Apr. 30, 2013
Revenue Recognition [Line Items]
Amounts received for reimbursement of travel and other out-of-pocket expenses	$ 450,000.0	$ 476,000.0	$ 1,700,000	$ 1,700,000
Unbilled amounts	4,027,000		4,027,000		3,741,000
Unbilled License Fees
Revenue Recognition [Line Items]
Unbilled amounts	1,600,000		1,600,000		1,100,000
Unbilled Services Revenues
Revenue Recognition [Line Items]
Unbilled amounts	$ 2,400,000		$ 2,400,000		$ 2,700,000
Minimum
Revenue Recognition [Line Items]
Contractual period of maintenance contract			1 year
Maximum
Revenue Recognition [Line Items]
Contractual period of maintenance contract			3 years