Financial Statement Components - Selected Financial Statement Components (Details) - USD ($) $ in Thousands	Mar. 30, 2019	Dec. 29, 2018	Mar. 31, 2018	Dec. 30, 2017
Inventories:
Raw materials and sub-assemblies	$ 34,922	$ 31,434
Work in process	20,171	22,383
Finished goods	8,377	8,098
Inventories	63,470	61,915
Inventories-delivered systems	349	180
Total inventories	63,819	62,095
Property, plant and equipment, net:
Total property, plant and equipment, gross	95,198	95,517
Accumulated depreciation and amortization	(44,666)	(47,617)
Total property, plant and equipment, net	50,532	47,900
Other Current Liabilities:
Accrued warranty	3,848	4,379	$ 4,643	$ 4,863
Accrued taxes	851	1,738
Customer deposits	321	293
Accrued professional services	469	448
Third party commissions	168	1,382
Other	1,202	1,181
Total other current liabilities	6,859	9,421
Land [Member]
Property, plant and equipment, net:
Total property, plant and equipment, gross	15,570	15,571
Building and improvements [Member]
Property, plant and equipment, net:
Total property, plant and equipment, gross	21,423	21,354
Machinery and equipment [Member]
Property, plant and equipment, net:
Total property, plant and equipment, gross	36,309	39,898
Furniture and fixtures [Member]
Property, plant and equipment, net:
Total property, plant and equipment, gross	2,578	2,551
Software [Member]
Property, plant and equipment, net:
Total property, plant and equipment, gross	10,309	10,116
Capital in progress [Member]
Property, plant and equipment, net:
Total property, plant and equipment, gross	$ 9,009	$ 6,027