Presentation and Summary of Significant Accounting Policies - Summary of Effect of Adopting Topic 606 on Condensed Consolidated Balance Sheet (Details) - USD ($) $ in Thousands	Apr. 30, 2019	May 01, 2018	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2016
Current assets:
Cash and cash equivalents	$ 61,288	$ 52,794	$ 52,794
Investments	24,710	26,121	26,121
Trade accounts receivable, net
Billed	18,819	18,643	18,643
Unbilled	1,475	3,815	3,375
Prepaid expenses and other current assets	6,210	6,718	6,592
Total current assets	112,502	108,091	107,525
Investments—Noncurrent	2,484	8,893	8,893
Property and equipment, net	3,585	3,034	3,034
Capitalized software, net	11,063	9,728	9,728
Goodwill	25,888	25,888	25,888	$ 19,549
Other intangibles, net	2,732	5,120	5,120	3,399
Other assets	3,056	4,102	2,777
Total assets	161,310	164,856	162,965
Current liabilities:
Accounts payable	2,448	1,974	1,974
Accrued compensation and related costs	2,561	6,310	6,310
Dividends payable	3,434	3,367	3,367
Other current liabilities	1,375	1,326	1,246
Deferred revenue	33,283	32,705	33,226
Total current liabilities	43,101	45,682	46,123
Deferred income taxes	3,514	3,194	2,615
Long-term deferred revenue	0	147	147
Other long-term liabilities	88	1,496	1,496
Total liabilities	46,703	50,519	50,381
Shareholders’ equity:
Additional paid-in capital	138,315	131,258	131,258
Retained (deficit) earnings	(1,729)	5,119	3,366
Class A treasury stock	(25,559)	(25,559)	(25,559)
Total shareholders’ equity	114,607	114,337	112,584	$ 103,750	$ 94,894
Total liabilities and shareholders’ equity	161,310	164,856	162,965
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Current assets:
Cash and cash equivalents	0	0
Investments	0	0
Trade accounts receivable, net
Billed	0	0
Unbilled	(289)	440
Prepaid expenses and other current assets	(102)	126
Total current assets	(391)	566
Investments—Noncurrent	0	0
Property and equipment, net	0	0
Capitalized software, net	0	0
Goodwill	0	0
Other intangibles, net	0	0
Other assets	(1,413)	1,325
Total assets	(1,804)	1,891
Current liabilities:
Accounts payable	0	0
Accrued compensation and related costs	0	0
Dividends payable	0	0
Other current liabilities	(80)	80
Deferred revenue	0	(521)
Total current liabilities	(80)	(441)
Deferred income taxes	(512)	579
Long-term deferred revenue	0	0
Other long-term liabilities	0	0
Total liabilities	(592)	138
Shareholders’ equity:
Additional paid-in capital	0	0
Retained (deficit) earnings	(1,212)	1,753
Class A treasury stock	0	0
Total shareholders’ equity	(1,212)	1,753
Total liabilities and shareholders’ equity	(1,804)	1,891
Calculated under Revenue Guidance in Effect before Topic 606
Current assets:
Cash and cash equivalents	61,288
Investments	24,710
Trade accounts receivable, net
Billed	18,819
Unbilled	1,186
Prepaid expenses and other current assets	6,108
Total current assets	112,111
Investments—Noncurrent	2,484
Property and equipment, net	3,585
Capitalized software, net	11,063
Goodwill	25,888
Other intangibles, net	2,732
Other assets	1,643
Total assets	159,506
Current liabilities:
Accounts payable	2,448
Accrued compensation and related costs	2,561
Dividends payable	3,434
Other current liabilities	1,295
Deferred revenue	33,283
Total current liabilities	43,021
Deferred income taxes	3,002
Long-term deferred revenue	0
Other long-term liabilities	88
Total liabilities	46,111
Shareholders’ equity:
Additional paid-in capital	138,315
Retained (deficit) earnings	(2,941)
Class A treasury stock	(25,559)
Total shareholders’ equity	113,395
Total liabilities and shareholders’ equity	159,506
Class A Common Shares
Shareholders’ equity:
Common stock value	3,398	3,314	3,314
Class A Common Shares | Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Shareholders’ equity:
Common stock value	0	0
Class A Common Shares | Calculated under Revenue Guidance in Effect before Topic 606
Shareholders’ equity:
Common stock value	3,398
Class B Common Shares
Shareholders’ equity:
Common stock value	182	205	$ 205
Class B Common Shares | Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Shareholders’ equity:
Common stock value	0	$ 0
Class B Common Shares | Calculated under Revenue Guidance in Effect before Topic 606
Shareholders’ equity:
Common stock value	$ 182