Presentation and Summary of Significant Accounting Policies - Summary of Effect of Adopting Topic 606 on Condensed Consolidated Statement of Operations (Detail) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		6 Months Ended
		Oct. 31, 2018	Oct. 31, 2017	Oct. 31, 2018	Oct. 31, 2017
Revenues
Revenues		$ 28,033	$ 26,337	$ 55,432	$ 53,222
Cost of revenues:
Cost of revenues		13,366	12,331	27,013	23,992
Gross margin		14,667	14,006	28,419	29,230
Research and development		3,332	2,643	7,007	5,151
Sales and marketing		5,304	4,437	10,484	9,670
General and administrative		4,408	3,616	8,601	7,155
Amortization of acquisition-related intangibles		97	68	194	391
Total operating expenses		13,141	10,764	26,286	22,367
Operating income		1,526	3,242	2,133	6,863
Other income:
Interest income		524	354	1,027	717
Other, net		(714)	322	(464)	558
Earnings before income taxes		1,336	3,918	2,696	8,138
Income tax expense (benefit)		93	1,438	68	2,933
Net earnings		$ 1,243	$ 2,480	$ 2,628	$ 5,205
Earnings per common share:
Basic	[1]	$ 0.04	$ 0.08	$ 0.09	$ 0.17
Diluted	[1]	$ 0.04	$ 0.08	$ 0.08	$ 0.17
Balances under Prior GAAP
Revenues
Revenues		$ 28,472		$ 55,487
Cost of revenues:
Cost of revenues		13,366		27,013
Gross margin		15,106		28,474
Research and development		3,332		7,007
Sales and marketing		5,368		10,577
General and administrative		4,408		8,601
Amortization of acquisition-related intangibles		97		194
Total operating expenses		13,204		26,379
Operating income		1,902		2,095
Other income:
Interest income		524		1,027
Other, net		(714)		(464)
Earnings before income taxes		1,712		2,658
Income tax expense (benefit)		164		63
Net earnings		$ 1,548		$ 2,595
Earnings per common share:
Basic		$ 0.05		$ 0.09
Diluted		$ 0.05		$ 0.08
Accounting Standards Update 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606
Revenues
Revenues		$ 439		$ 55
Cost of revenues:
Gross margin		439		55
Sales and marketing		63		93
Total operating expenses		63		93
Operating income		376		(38)
Other income:
Earnings before income taxes		376		(38)
Income tax expense (benefit)		71		(5)
Net earnings		$ 305		(33)
Earnings per common share:
Basic		$ 0.01
Diluted		$ 0.01
License
Revenues
Revenues		$ 2,012	$ 2,449	3,714	$ 6,464
Cost of revenues:
Cost of revenues		1,760	1,651	3,474	2,966
License | Balances under Prior GAAP
Revenues
Revenues		2,403		3,659
Cost of revenues:
Cost of revenues		1,760		3,474
License | Accounting Standards Update 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606
Revenues
Revenues		391		(55)
Subscription Fees
Revenues
Revenues		3,341	2,041	6,509	3,660
Cost of revenues:
Cost of revenues		1,289	903	2,356	1,749
Subscription Fees | Balances under Prior GAAP
Revenues
Revenues		3,343		6,513
Cost of revenues:
Cost of revenues		1,289		2,356
Subscription Fees | Accounting Standards Update 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606
Revenues
Revenues		2		4
Professional Services and Other
Revenues
Revenues		11,056	11,008	22,064	21,431
Cost of revenues:
Cost of revenues		8,103	7,488	16,771	14,761
Professional Services and Other | Balances under Prior GAAP
Revenues
Revenues		11,102		22,170
Cost of revenues:
Cost of revenues		8,103		16,771
Professional Services and Other | Accounting Standards Update 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606
Revenues
Revenues		46		106
Maintenance
Revenues
Revenues		11,624	10,839	23,145	21,667
Cost of revenues:
Cost of revenues		2,214	$ 2,288	4,412	$ 4,516
Maintenance | Balances under Prior GAAP
Revenues
Revenues		11,624		23,145
Cost of revenues:
Cost of revenues		$ 2,214		$ 4,412

[1] Basic per share amounts are the same for Class A and Class B shares. Diluted per share amounts for Class A shares are shown above. Diluted earnings per share for Class B shares under the two-class method are $0.04 and $0.08 for the three months ended October 31, 2018 and 2017, and $0.09 and $0.17 for the six months ended October 31, 2018 and 2017, respectively. See Note D to the Condensed Consolidated Financial Statements.