Income Taxes Reconciliation (Details) - USD ($) $ in Thousands			4 Months Ended	8 Months Ended	12 Months Ended
	Jan. 01, 2018	Dec. 31, 2017	Apr. 30, 2018	Dec. 31, 2017	Apr. 30, 2019	Apr. 30, 2018	Apr. 30, 2017
Income Taxes
U.S. federal statutory income tax rate (as a percent)	21.00%	35.00%	21.00%	35.00%	21.00%	30.40%	34.00%
State and local income taxes, net of federal benefit (as a percent)					(2.20%)	(2.20%)	(1.70%)
R&D and other tax credits (as a percent)					(8.10%)	(7.00%)	(10.80%)
Valuation allowance (as a percent)					3.70%	4.90%	3.80%
Foreign rate differential						0.10%
Return to provision adjustments (as a percent)					(0.30%)	(0.10%)	(0.30%)
Permanent items (as a percent)					0.80%	(2.70%)	(2.30%)
Foreign derived intangible income (as a percent)					(3.70%)
Excess benefit of stock options (as a percent)					(3.10%)	(4.40%)	(1.00%)
Tax Act (as a percent)						10.40%
Other (as a percent)					1.10%	0.60%	(0.60%)
Effective income tax rate (as a percent)					9.20%	30.00%	21.10%
Current:
Federal					$ 1,953	$ 6,010	$ 4,336
State					228	900	243
Current					2,181	6,910	4,579
Deferred:
Federal					1,945	3,272	(66)
State					551	(330)	280
Foreign					(36)	(52)	(35)
Deferred					2,460	2,890	179
Total income tax expense (benefit)					4,641	9,800	$ 4,758
Deferred income tax assets:
Accrued expenses			$ 5,771		5,206	5,771
Allowances, reserves, and other			2,100		2,729	2,100
Unrealized loss on securities			25			25
Net operating loss and credit carry-forwards			12,361		13,208	12,361
Intangibles basis			94		125	94
Total deferred income tax assets			20,351		21,268	20,351
Deferred income tax liabilities:
Fixed asset basis			(682)		(425)	(682)
Revenue recognition			326		(2,909)	326
Total deferred income tax liabilities			(356)		(3,334)	(356)
Valuation allowance			(8,568)		(11,278)	(8,568)
Net deferred tax assets			$ 11,427		$ 6,656	$ 11,427