Restructuring Costs - Narrative (Details) ft² in Thousands, $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018 USD ($)	Jul. 01, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jul. 01, 2017 USD ($)	Dec. 30, 2017 USD ($) ft² Employee
Restructuring Cost and Reserve [Line Items]
Restructuring costs	$ 569	$ 0	$ 1,339	$ 0
Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs			(55)
Restructuring Plan 2017 [Member]
Restructuring Cost and Reserve [Line Items]
Manufacturing facility square footage (in sqft) | ft²					160
Expected restructuring costs	1,745		1,745
Restructuring costs			1,339
Expected remaining restructuring costs	$ 203		203
Restructuring Plan 2017 [Member] | Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs			(55)		$ 203
Restructuring Plan 2017 [Member] | Relocation Of Machinery And Equipment And Administrative Offices [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs			1,018
Restructuring Plan 2017 [Member] | Employee Retention, Facility Closing, And Other Closure Costs [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs			$ 376
Restructuring Plan 2017 [Member] | United States [Member]
Restructuring Cost and Reserve [Line Items]
Number of positions eliminated related to restructuring | Employee					4
Restructuring Plan 2017 [Member] | Sweden [Member]
Restructuring Cost and Reserve [Line Items]
Number of positions eliminated related to restructuring | Employee					6