Presentation and Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Apr. 30, 2019 USD ($)	Apr. 30, 2018 USD ($) Segment Group CompensationPlan $ / shares	Apr. 30, 2017 USD ($)	Apr. 30, 2016 USD ($)
Accounting Policies [Line Items]
Number of major business segments | Segment		3
Number of major product and service groups | Group		6
Amounts received for reimbursement of travel and other out-of-pocket expenses		$ 1,900,000	$ 2,100,000	$ 2,400,000
Unbilled amounts		3,375,000	2,811,000
Cash equivalents		47,000,000	62,600,000
Total amounts of expense/(recovery) to operations for doubtful accounts		24,000	39,000	0
Depreciation and amortization expense		492,000	731,000	807,000
Amortization of acquisition-related intangibles		$ 580,000	1,041,000	272,000
Number of stock compensation plans | CompensationPlan		4
Stock-based compensation expense		$ 1,467,000	1,428,000	1,593,000
Income tax benefit		547,000	528,000	586,000
Advertising expense		$ 2,400,000	2,300,000	2,100,000
Number of reportable segments | Segment		3
Computers Equipment And Software
Accounting Policies [Line Items]
Estimated useful lives of assets		3 years
Office furniture and equipment
Accounting Policies [Line Items]
Estimated useful lives of assets		7 years
Building
Accounting Policies [Line Items]
Estimated useful lives of assets		30 years
Operating Expense
Accounting Policies [Line Items]
Amortization of acquisition-related intangibles		$ 580,000	1,041,000	272,000
Cost of License Fees
Accounting Policies [Line Items]
Amortization of acquisition-related intangibles		$ 1,269,000	618,000	618,000
Class A Common Shares
Accounting Policies [Line Items]
Dividends preference, per share | $ / shares		$ 0.05
Capitalized Software
Accounting Policies [Line Items]
Intangible assets amortized period		3 years
Finite-Lived Intangible Assets [Member]
Accounting Policies [Line Items]
Amortization of acquisition-related intangibles		$ 1,849,000	1,659,000	$ 890,000
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09 | Scenario, Forecast
Accounting Policies [Line Items]
Total revenues	$ 1,200,000
Upfront recognition of revenue under new standard	70.00%
License Fees
Accounting Policies [Line Items]
Unbilled amounts		800,000	1,000,000
Services Revenues
Accounting Policies [Line Items]
Unbilled amounts		$ 2,500,000	$ 1,800,000
Minimum
Accounting Policies [Line Items]
Contractual period of maintenance contract		1 year
Minimum | Other Intangible Assets
Accounting Policies [Line Items]
Intangible assets amortized period		1 year
Maximum
Accounting Policies [Line Items]
Contractual period of maintenance contract		3 years
Maximum | Other Intangible Assets
Accounting Policies [Line Items]
Intangible assets amortized period		8 years