Financial Statement Components - Selected Financial Statement Components (Details) - USD ($) $ in Thousands	Dec. 30, 2017	Dec. 31, 2016	Dec. 26, 2015
Inventories:
Raw materials and sub-assemblies	$ 32,187	$ 23,506
Work in process	13,498	10,347
Finished goods	7,175	4,984
Inventories	52,860	38,837
Inventories-delivered systems	1,534	2,457
Total inventories	54,394	41,294
Property, plant and equipment, net:
Total property, plant and equipment, gross	89,229	86,545
Accumulated depreciation and amortization	(44,419)	(42,319)
Total property, plant and equipment, net	44,810	44,226
Other Current Liabilities:
Accrued warranty	4,863	3,838	$ 4,504
Accrued taxes	813	706
Customer deposits		581
Accrued professional services	534	424
Accrued royalties		1,233
Other	1,039	1,265
Total other current liabilities	7,249	8,047
Land [Member]
Property, plant and equipment, net:
Total property, plant and equipment, gross	15,573	15,568
Building and improvements [Member]
Property, plant and equipment, net:
Total property, plant and equipment, gross	20,880	20,532
Machinery and equipment [Member]
Property, plant and equipment, net:
Total property, plant and equipment, gross	36,380	35,659
Furniture and fixtures [Member]
Property, plant and equipment, net:
Total property, plant and equipment, gross	2,420	2,282
Software [Member]
Property, plant and equipment, net:
Total property, plant and equipment, gross	9,558	9,756
Capital in progress [Member]
Property, plant and equipment, net:
Total property, plant and equipment, gross	$ 4,418	$ 2,748