Financial Statement Components - Selected Financial Statement Components (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Jul. 01, 2017	Dec. 31, 2016	Sep. 24, 2016	Jun. 25, 2016	Dec. 26, 2015
Inventories:
Raw materials and sub-assemblies	$ 31,772		$ 23,506
Work in process	18,280		10,347
Finished goods	4,968		4,984
Inventories	55,020		38,837
Inventories-delivered systems	3,320		2,457
Total inventories	58,340		41,294
Property, plant and equipment, net:
Total property, plant and equipment, gross	85,023		86,545
Accumulated depreciation and amortization	(42,706)		(42,319)
Total property, plant and equipment, net	42,317		44,226
Other Current Liabilities:
Accrued warranty	4,542	$ 4,602	3,838	$ 4,185	$ 4,556	$ 4,504
Customer deposits	67		581
Retrofit liability	353		432
Accrued professional services	784		424
Accrued royalties	60		1,233
Other	1,898		1,539
Total other current liabilities	7,704		8,047
Land [Member]
Property, plant and equipment, net:
Total property, plant and equipment, gross	15,571		15,568
Building and improvements [Member]
Property, plant and equipment, net:
Total property, plant and equipment, gross	20,649		20,532
Machinery and equipment [Member]
Property, plant and equipment, net:
Total property, plant and equipment, gross	35,428		35,659
Furniture and fixtures [Member]
Property, plant and equipment, net:
Total property, plant and equipment, gross	2,289		2,282
Software [Member]
Property, plant and equipment, net:
Total property, plant and equipment, gross	9,261		9,756
Capital in progress [Member]
Property, plant and equipment, net:
Total property, plant and equipment, gross	$ 1,825		$ 2,748