Income Taxes Reconciliation (Details) - USD ($) $ in Thousands			12 Months Ended
	Jan. 01, 2018	Dec. 31, 2017	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2016
Income Taxes
U.S. federal statutory income tax rate (as a percent)	21.00%	35.00%	30.40%	34.00%	35.00%
State and local income taxes, net of federal benefit (as a percent)			(2.00%)	(1.90%)	(5.30%)
R&D and other tax credits (as a percent)			(6.70%)	(11.70%)	(19.20%)
Valuation allowance (as a percent)			4.70%	4.10%	7.30%
Foreign rate differential			0.10%
Return to provision adjustments (as a percent)			(0.10%)	(0.30%)	2.10%
Permanent items (as a percent)			(6.90%)	(3.60%)	(3.10%)
Tax Act			10.00%
Other (as a percent)			0.60%	(0.80%)	(0.70%)
Effective income tax rate (as a percent)			30.10%	19.80%	16.10%
Current:
Federal			$ 6,363	$ 3,745	$ 5,388
State			925	215	406
Current			7,288	3,960	5,794
Deferred:
Federal			3,272	(66)	(2,814)
State			(331)	279	3
Foreign			(52)	(35)
Deferred			2,889	178	(2,811)
Total income tax expense (benefit)			10,177	4,138	$ 2,983
Deferred income tax assets:
Accrued expenses			5,771	7,074
Allowances, reserves, and other			2,100	1,801
Unrealized loss on securities			25	74
Net operating loss and credit carry-forwards			12,361	11,854
Intangibles basis			94	43
Total deferred income tax assets			20,351	20,846
Deferred income tax liabilities:
Other				29
Fixed asset basis			(682)	(428)
Total deferred income tax liabilities			(682)	(457)
Valuation allowance			(8,568)	(5,416)
Net deferred tax assets			$ 11,101	$ 14,973