6. Employee Retirement Benefit Plans (Details) $ in Thousands	3 Months Ended
Mar. 29, 2019 USD ($)
Text Block [Abstract]
Pension Plan Settlement Agreement, Payment Schedule	Eight installments of $750 to the Pension Benefit Guaranty Corporation due annually on October 31
Contribution by Employer	$ 438
Imputed interest expense rate	7.00%

Amount of contributions received and expected to be received by defined benefit plan from employer in current fiscal year.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2709-114920

Name:	us-gaap_DefinedBenefitPlanExpectedFutureEmployerContributionsCurrentFiscalYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant