General (Details 3) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 27, 2018	Sep. 28, 2017	Sep. 27, 2018	Sep. 28, 2017
Service cost	$ 231	$ 192	$ 694	$ 574
Interest cost	341	339	1,023	1,017
Net amortization of prior service cost and actuarial loss	156	89	466	267
Net periodic pension cost	$ 728	$ 620	$ 2,183	$ 1,858

Amount of cost for actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration