General (Details Textual) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 27, 2018	Sep. 28, 2017	Sep. 27, 2018	Sep. 28, 2017	Dec. 28, 2017
Summary of Significant Accounting Policies [Line Items]
Depreciation	$ 14,556,000	$ 12,946,000	$ 43,037,000	$ 37,368,000
Percentage Of Cash Dividends	110.00%
Interest Rate Fair Value Hedge Asset at Fair Value	$ 444,000		444,000		$ 13,000
Trading Securities, Fair Value Disclosure	5,762,000		5,762,000		$ 4,053,000
Reimbursed Costs	$ 9,088,000	8,557,000	25,776,000	23,424,000
Decrease in net cash used in investing activities			$ (46,096,000)	(82,123,000)
Post Employment Benefits Reclassified Operating Income To Other Expense		$ 428,000		1,284,000
Accounting Standards Update 2016-18 [Member] | Scenario, Adjustment [Member]
Summary of Significant Accounting Policies [Line Items]
Decrease in net cash used in investing activities				$ (2,438,000)