Presentation and Summary of Significant Accounting Policies - Additional Information (Details) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Apr. 30, 2019 USD ($)	Jan. 31, 2019 USD ($)	Oct. 31, 2018 USD ($)	Jul. 31, 2018 USD ($)	Apr. 30, 2018 USD ($)	Jan. 31, 2018 USD ($)	Oct. 31, 2017 USD ($)	Jul. 31, 2017 USD ($)	Apr. 30, 2019 USD ($) Segment CompensationPlan Group $ / shares	Apr. 30, 2018 USD ($)	Apr. 30, 2017 USD ($)	May 01, 2019 USD ($)	May 01, 2018 USD ($)
Accounting Policies [Line Items]
Number of major product and service groups | Group									6
Number of major business segments | Segment									3
Amounts received for reimbursement of travel and other out-of-pocket expenses									$ 1,400	$ 1,900	$ 2,100
Revenue recognized and included in deferred revenue									33,300
Amortization of sales commissions									1,300
Unbilled	$ 1,475				$ 3,375				1,475	3,375			$ 3,815
Cash equivalents	56,600				47,000				56,600	47,000
Total amounts of expense/(recovery) to operations for doubtful accounts									0	24	39,000,000
Depreciation and amortization expense									700	500	700
Amortization of acquisition-related intangibles									388	580	1,041
Remaining performance obligations	62,400								62,400
Deferred commissions	2,300				2,500				2,300	2,500
Total revenues	$ 26,271	$ 27,003	$ 28,033	$ 27,399	29,363	$ 30,117	$ 26,337	$ 26,886	$ 108,706	112,703	106,286
Period of economic benefit	6 years								6 years
Number of stock compensation plans | CompensationPlan									1
Stock-based compensation expense									$ 1,751	1,467	1,428
Income tax benefit (shortfall)									300	(39)	45
Advertising expense									$ 2,300	2,400	2,300
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									$ 400	600	1,000
Cost of License Fees
Accounting Policies [Line Items]
Amortization of acquisition-related intangibles									$ 2,000	1,200	700
Class A Common Shares
Accounting Policies [Line Items]
Dividends preference (in usd per share) | $ / shares									$ 0.05
Difference between Revenue Guidance in Effect before and after Topic 606
Accounting Policies [Line Items]
Total revenues									$ 1,200
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Accounting Policies [Line Items]
Unbilled	$ (289)								(289)				$ 440
Amortization of acquisition-related intangibles									0
Total revenues									$ 774
Upfront recognition of revenue under new standard									70.00%
Sales commission capitalized	1,100								$ 1,100
Capitalized Software
Accounting Policies [Line Items]
Intangible assets amortized period									3 years
Finite-Lived Intangible Assets
Accounting Policies [Line Items]
Amortization of acquisition-related intangibles									$ 2,400	1,800	$ 1,700
License Fees
Accounting Policies [Line Items]
Unbilled	400				800				400	800
Services Revenues
Accounting Policies [Line Items]
Unbilled	$ 1,100				$ 2,500				$ 1,100	$ 2,500
Minimum
Accounting Policies [Line Items]
Contractual period of maintenance contract									1 year
Minimum | Accounting Standards Update 2016-02 | Subsequent Event | Scenario, Forecast
Accounting Policies [Line Items]
Operating lease, right-of-use asset												$ 28,000
Operating lease liability												2,700
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 | Accounting Standards Update 2016-02 | Subsequent Event | Scenario, Forecast
Accounting Policies [Line Items]
Operating lease, right-of-use asset												30,000
Operating lease liability												$ 3,000
Maximum | Other Intangible Assets
Accounting Policies [Line Items]
Intangible assets amortized period									8 years