Unbilled amounts due for services rendered or to be rendered, actions taken or to be taken, or a promise to refrain from taking certain actions in accordance with the terms of a legally binding agreement between the entity and, at a minimum, one other party. An example would be amounts associated with contracts or programs where the recognized revenue for performance thereunder exceeds the amounts billed under the terms thereof as of the date of the balance sheet.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.3(c)(3))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 912
-SubTopic 310
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=68054760&loc=d3e55302-109406

Name:	us-gaap_UnbilledContractsReceivable
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Revenue Recognition - Additional Information (Detail) - USD ($)	3 Months Ended
	Jul. 31, 2017	Jul. 31, 2016	Apr. 30, 2017
Revenue Recognition [Line Items]
Amounts received for reimbursement of travel and other out-of-pocket expenses	$ 525,000	$ 632,000
Unbilled amounts	2,377,000		$ 2,811,000
Unbilled License Fees
Revenue Recognition [Line Items]
Unbilled amounts	300,000		1,000,000
Unbilled Services Revenues
Revenue Recognition [Line Items]
Unbilled amounts	$ 2,100,000		$ 1,800,000
Minimum
Revenue Recognition [Line Items]
Contractual period of maintenance contract	1 year
Maximum
Revenue Recognition [Line Items]
Contractual period of maintenance contract	3 years