Financial Statement Components - Selected Financial Statement Components (Details) - USD ($) $ in Thousands	Jun. 29, 2019	Mar. 30, 2019	Dec. 29, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 30, 2017
Inventories:
Raw materials and sub-assemblies	$ 35,880		$ 31,434
Work in process	21,061		22,383
Finished goods	9,689		8,098
Inventories	66,630		61,915
Inventories-delivered systems	1,010		180
Total inventories	67,640		62,095
Property, plant and equipment, net:
Total property, plant and equipment, gross	98,649		95,517
Accumulated depreciation and amortization	(45,870)		(47,617)
Total property, plant and equipment, net	52,779		47,900
Other Current Liabilities:
Accrued warranty	3,755	$ 3,848	4,379	$ 4,906	$ 4,643	$ 4,863
Accrued taxes	965		1,738
Customer deposits	388		293
Accrued professional services	625		448
Third party commissions	249		1,382
Other	1,326		1,181
Total other current liabilities	7,308		9,421
Land [Member]
Property, plant and equipment, net:
Total property, plant and equipment, gross	15,570		15,571
Machinery and equipment [Member]
Property, plant and equipment, net:
Total property, plant and equipment, gross	37,608		39,898
Building and improvements [Member]
Property, plant and equipment, net:
Total property, plant and equipment, gross	26,344		21,354
Software [Member]
Property, plant and equipment, net:
Total property, plant and equipment, gross	10,377		10,116
Furniture and fixtures [Member]
Property, plant and equipment, net:
Total property, plant and equipment, gross	2,471		2,551
Leasehold improvements [Member]
Property, plant and equipment, net:
Total property, plant and equipment, gross	1,774
Capital in progress [Member]
Property, plant and equipment, net:
Total property, plant and equipment, gross	$ 4,505		$ 6,027