Defined Benefit Pension Plans (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 29, 2018	Jun. 30, 2017	Jun. 29, 2018	Jun. 30, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	[1]	$ 139	$ 129	$ 277	$ 258
Interest cost	[2]	15	14	29	28
Expected return on plan assets	[2]	(28)	(24)	(54)	(47)
Net amortization of transitional obligation	[2],[3]	2	3	5	6
Prior service credit	[2],[3]	(5)	(2)	(11)	(4)
Actuarial loss recognized in current period	[2],[3]	29	18	57	35
Net periodic pension cost		$ 152	$ 138	$ 303	$ 276

[1] Recognized in selling general and administrative expenses on the Condensed Consolidated Statements of Operations.

[2] For 2018, recognized in other income, net, and for 2017, recognized in selling, general and administrative on the Condensed Consolidated Statements of Operations.

[3] Amounts reclassified from accumulated other comprehensive loss.