Income Taxes - Tax Effects of Temporary Differences That Give Rise to Significant Portions of Deferred Tax Assets and Deferred Tax Liabilities (Details) - USD ($) $ in Thousands	Apr. 30, 2019	Apr. 30, 2018
Deferred tax assets
Accruals and expenses not deducted for tax purposes	$ 328	$ 339
State net operating loss carryforwards	217	226
Fixed asset basis differences	831	883
Nonqualified stock options	858	762
Deferred revenue	0	53
Total gross deferred tax assets	2,234	2,263
Less valuation allowance	(160)	(170)
Net deferred tax	2,074	2,093
Deferred tax liabilities
Capitalized computer software development costs	(2,766)	(2,432)
Net gains/losses on trading securities	(1,183)	(938)
Goodwill and intangible assets basis differences	(639)	(601)
Deferred agent commissions	(1,000)	(737)
Total gross deferred tax liabilities	(5,588)	(4,708)
Net deferred tax liabilities	$ (3,514)	$ (2,615)