General (Details Textual) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 28, 2018	Jun. 29, 2017	Jun. 28, 2018	Jun. 29, 2017	Dec. 28, 2017
Summary of Significant Accounting Policies [Line Items]
Depreciation	$ 14,445,000	$ 12,250,000	$ 28,481,000	$ 24,422,000
Percentage Of Cash Dividends			110.00%
Interest Rate Fair Value Hedge Asset at Fair Value	119,000		$ 119,000		$ 13,000
Trading Securities, Fair Value Disclosure	4,769,000		4,769,000		$ 4,053,000
Reimbursed Costs	$ 8,916,000	7,365,000	16,688,000	14,867,000
Net Cash Provided by (Used in) Investing Activities			$ (33,494,000)	(50,367,000)
Postemployment Benefits Reclassified Operating Income To Other Expense		$ 428,000		856,000
Accounting Standards Update 2016-18 [Member] | Scenario, Adjustment [Member]
Summary of Significant Accounting Policies [Line Items]
Net Cash Provided by (Used in) Investing Activities				$ 2,086,000