Presentation and Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Apr. 30, 2017 USD ($) Segment CompensationPlan Group $ / shares	Apr. 30, 2016 USD ($)	Apr. 30, 2015 USD ($)
Accounting Policies [Line Items]
Number of major business segments | Segment	3
Number of major product and service groups | Group	4
Amounts received for reimbursement of travel and other out-of-pocket expenses	$ 2,100,000	$ 2,400,000	$ 2,700,000
Unbilled amounts	2,811,000	3,444,000
Cash equivalents	62,600,000	46,000,000
Total amounts of expense/(recovery) to operations for doubtful accounts	39,000	0	178,000
Depreciation and amortization expense	731,000	807,000	1,193,000
Amortization of acquisition-related intangibles	$ 1,041,000	272,000	394,000
Goodwill, impairment charge			0
Number of stock compensation plans | CompensationPlan	4
Stock-based compensation expense	$ 1,428,000	1,593,000	1,530,000
Income tax benefit	528,000	586,000	542,000
Excess tax benefits from stock-based compensation			384,000
Advertising expense	$ 2,000,000	2,100,000	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	$ 1,041,000	272,000	394,000
Cost of License Fees
Accounting Policies [Line Items]
Amortization of acquisition-related intangibles	$ 618,000	618,000	$ 576,000
Class A Common Shares
Accounting Policies [Line Items]
Dividends preference, per share | $ / shares	$ 0.05
Goodwill | Income Approach Valuation Technique | Discounted Cash Flows Valuation Technique
Accounting Policies [Line Items]
Fair value input, valuation technique, weight			50.00%
Goodwill | Market Approach Valuation Technique | Comparable Transaction Methodology Valuation Technique
Accounting Policies [Line Items]
Fair value input, valuation technique, weight			15.00%
Goodwill | Market Approach Valuation Technique | Comparable Company Methodology Valuation Technique
Accounting Policies [Line Items]
Fair value input, valuation technique, weight			35.00%
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	$ 1,659,000	890,000	$ 970,000
Unbilled License Fees
Accounting Policies [Line Items]
Unbilled amounts	1,000,000	1,500,000
Unbilled Services Revenues
Accounting Policies [Line Items]
Unbilled amounts	$ 1,800,000	$ 1,900,000
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