Income Taxes - Tax Effects of Temporary Differences That Give Rise to Significant Portions of Deferred Tax Assets and Deferred Tax Liabilities (Detail) - USD ($) $ in Thousands	Apr. 30, 2018	Apr. 30, 2017
Deferred tax assets:
Accruals and expenses not deducted for tax purposes	$ 339	$ 461
State net operating loss carryforwards	226	295
Fixed asset basis differences	883	1,384
Nonqualified stock options	762	1,679
Deferred revenue	53	234
Total gross deferred tax assets	2,263	4,053
Less valuation allowance	170	166
Net deferred tax	2,093	3,887
Deferred tax liabilities:
Capitalized computer software development costs	(2,432)	(3,298)
Net gains/losses on trading securities	(938)	(1,019)
Goodwill and intangible assets basis differences	(601)	(939)
Deferred agent commissions	(737)	(625)
Total gross deferred tax liabilities	(4,708)	(5,881)
Net deferred tax liabilities	$ (2,615)	$ (1,994)