Financial Statement Components - Selected Financial Statement Components (Details) - USD ($) $ in Thousands	Sep. 28, 2019	Jun. 29, 2019	Dec. 29, 2018	Sep. 29, 2018	Jun. 30, 2018	Dec. 30, 2017
Inventories:
Raw materials and sub-assemblies	$ 38,219		$ 31,434
Work in process	23,602		22,383
Finished goods	7,870		8,098
Inventories	69,691		61,915
Inventories-delivered systems	117		180
Total inventories	69,808		62,095
Property, plant and equipment, net:
Total property, plant and equipment, gross	100,162		95,517
Accumulated depreciation and amortization	(47,713)		(47,617)
Total property, plant and equipment, net	52,449		47,900
Other Current Liabilities:
Accrued warranty	4,393	$ 3,755	4,379	$ 4,258	$ 4,906	$ 4,863
Accrued taxes	757		1,738
Customer deposits	114		293
Accrued professional services	1,458		448
Third party commissions	452		1,382
Other	1,528		1,181
Total other current liabilities	8,702		9,421
Land [Member]
Property, plant and equipment, net:
Total property, plant and equipment, gross	15,568		15,571
Machinery and equipment [Member]
Property, plant and equipment, net:
Total property, plant and equipment, gross	40,027		39,898
Building and improvements [Member]
Property, plant and equipment, net:
Total property, plant and equipment, gross	26,717		21,354
Software [Member]
Property, plant and equipment, net:
Total property, plant and equipment, gross	10,621		10,116
Furniture and fixtures [Member]
Property, plant and equipment, net:
Total property, plant and equipment, gross	2,276		2,551
Leasehold improvements [Member]
Property, plant and equipment, net:
Total property, plant and equipment, gross	3,599
Capital in progress [Member]
Property, plant and equipment, net:
Total property, plant and equipment, gross	$ 1,354		$ 6,027