Income Taxes - Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2019	Apr. 30, 2018	Apr. 30, 2017
Current:
Federal	$ 184	$ 2,298	$ 5,643
State	334	743	676
Total current income tax expense	518	3,041	6,319
Deferred:
Federal	256	321	558
State	64	300	117
Total deferred income tax expense	320	621	675
Income tax expense	$ 838	$ 3,662	$ 6,994