Marketable Securities (Schedule Of Marketable Securities) (Details) - USD ($) $ in Thousands	Jul. 01, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 55,086	$ 58,937
Gross Unrealized Holding Gains	8,073	8,693
Gross Unrealized Holding Losses	(100)	(459)
Fair Value	63,059	67,171
Equity Securities [Member] \| Fair Value, Inputs, Level 1 [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,198	1,198
Gross Unrealized Holding Gains	7,034	8,162
Gross Unrealized Holding Losses	0	0
Fair Value	8,232	9,360
Municipal Bonds [Member] \| Fair Value, Inputs, Level 2 [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	53,888	57,739
Gross Unrealized Holding Gains	1,039	531
Gross Unrealized Holding Losses	(100)	(459)
Fair Value	$ 54,827	$ 57,811

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=65884222&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-Topic 320
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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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