Commitments and Contingencies - Additional Information (Detail) - USD ($)	12 Months Ended
Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2016
Commitments and Contingencies Disclosure [Abstract]
Operating lease rent expense	$ 2,340,000	$ 2,225,000	$ 2,283,000

Amount of rent expense incurred for leased assets, including but not limited to, furniture and equipment, that is not directly or indirectly associated with the manufacture, sale or creation of a product or product line.

No definition available.

Name:	us-gaap_LeaseAndRentalExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration