New Pronouncements Adopted (Details 1) - USD ($) $ in Thousands	Jun. 29, 2018	Jan. 01, 2018	Dec. 31, 2017
Retained Earnings Adjustments [Line Items]
Unbilled receivables		$ 2,658	$ 0
Inventories	$ 209,204	218,293	220,352
Other liabilities and accrued items	27,182	28,105	28,044
Long-term deferred income taxes	210	326	213
Retained earnings	$ 553,523	536,541	$ 536,116
Adjustments for New Accounting Pronouncement [Member]
Retained Earnings Adjustments [Line Items]
Unbilled receivables		2,658
Inventories		(2,059)
Other liabilities and accrued items		61
Long-term deferred income taxes		113
Retained earnings		$ 425

Carrying value as of the balance sheet date of obligations incurred and payable, pertaining to costs that are statutory in nature, are incurred on contractual obligations, or accumulate over time and for which invoices have not yet been received or will not be rendered. Examples include taxes, interest, rent and utilities. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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