Marketable Securities (Details 2) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2018	Dec. 30, 2017
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Losses Less than 12 Consecutive Months	$ (17,288)	$ (8,590)
Fair Value Less than 12 Consecutive Months	867,996	749,831
Gross Unrealized Losses 12 Consecutive Months or Longer	(24,935)	(16,380)
Fair Value 12 Consecutive Months or Longer	556,051	573,976
U.S.Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Losses Less than 12 Consecutive Months	(202)	(111)
Fair Value Less than 12 Consecutive Months	19,748	12,966
Gross Unrealized Losses 12 Consecutive Months or Longer	(179)	(143)
Fair Value 12 Consecutive Months or Longer	6,319	6,371
Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Losses Less than 12 Consecutive Months	(243)	(168)
Fair Value Less than 12 Consecutive Months	16,022	16,097
Gross Unrealized Losses 12 Consecutive Months or Longer	(913)	(663)
Fair Value 12 Consecutive Months or Longer	25,723	25,972
Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Losses Less than 12 Consecutive Months	(711)	(503)
Fair Value Less than 12 Consecutive Months	17,631	19,628
Gross Unrealized Losses 12 Consecutive Months or Longer	(6,914)	(5,365)
Fair Value 12 Consecutive Months or Longer	140,289	153,835
Corporate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Losses Less than 12 Consecutive Months	(11,562)	(4,562)
Fair Value Less than 12 Consecutive Months	538,556	439,174
Gross Unrealized Losses 12 Consecutive Months or Longer	(15,555)	(9,228)
Fair Value 12 Consecutive Months or Longer	341,137	347,052
Municipal Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Losses Less than 12 Consecutive Months	(1,786)	(1,027)
Fair Value Less than 12 Consecutive Months	139,591	125,819
Gross Unrealized Losses 12 Consecutive Months or Longer	(1,371)	(977)
Fair Value 12 Consecutive Months or Longer	40,649	38,167
Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Losses Less than 12 Consecutive Months	(2,784)	(2,219)
Fair Value Less than 12 Consecutive Months	136,448	136,147
Gross Unrealized Losses 12 Consecutive Months or Longer	(3)	(4)
Fair Value 12 Consecutive Months or Longer	$ 1,934	$ 2,579

Amount of unrealized loss on securities classified as available-for-sale that have been in a loss position for twelve months or longer.

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Amount of unrealized loss on investments in available-for-sale securities that have been in a loss position for less than twelve months.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(2)
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This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for less than twelve months.

+ References

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