Income Taxes Reconciliation (Details) - USD ($) $ in Thousands		4 Months Ended	9 Months Ended	12 Months Ended
	Dec. 22, 2017	Apr. 30, 2018	Jan. 31, 2018	Apr. 30, 2020	Apr. 30, 2019	Apr. 30, 2018
Income Taxes
U.S. federal statutory income tax rate (as a percent)	35.00%	21.00%	35.00%	21.00%	21.00%	30.40%
State and local income taxes, net of federal benefit (as a percent)				(2.10%)	(2.20%)	(2.20%)
R&D and other tax credits (as a percent)				(6.80%)	(8.10%)	(7.00%)
Valuation allowance (as a percent)				3.40%	3.70%	4.90%
Foreign rate differential						0.10%
Return to provision adjustments (as a percent)				0.10%	(0.30%)	(0.10%)
Permanent items (as a percent)				0.70%	0.80%	(2.70%)
Foreign derived intangible income (as a percent)				(3.90%)	(3.70%)
Excess benefit of stock options (as a percent)				(1.50%)	(3.10%)	(4.40%)
Tax Act (as a percent)						10.40%
Other (as a percent)				0.20%	1.10%	0.60%
Effective income tax rate (as a percent)				11.10%	9.20%	30.00%
Current:
Federal				$ 3,005	$ 1,953	$ 6,010
State				390	228	900
Current				3,395	2,181	6,910
Deferred:
Federal				2,063	1,945	3,272
State				421	551	(330)
Foreign				(31)	(36)	(52)
Deferred				2,453	2,460	2,890
Total income tax expense (benefit)				5,848	4,641	$ 9,800
Deferred income tax assets:
Accrued expenses				3,337	3,559
Stock based compensaton				2,259	1,647
Allowances, reserves, and other				1,784	1,579
Outside basis difference				2,264	1,150
Unrealized loss on securities				9
Net operating loss and credit carry-forwards				12,832	13,208
Intangibles basis				605	125
Lease liability				2,282
Total deferred income tax assets				25,372	21,268
Deferred income tax liabilities:
Fixed asset basis				(1,218)	(425)
Revenue recognition				(3,112)	(2,909)
Right of use assets				(1,965)
Total deferred income tax liabilities				(6,295)	(3,334)
Valuation allowance				(14,149)	(11,278)
Net deferred tax assets				$ 4,928	$ 6,656