Marketable Securities (Details 1) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2018	Dec. 30, 2017
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost	$ 1,519,087	$ 1,446,428
Gross Unrealized Gains	66	262
Gross Unrealized Losses	(42,223)	24,970
Fair Value	1,476,930	1,421,720
U.S.Treasury Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost	29,439	19,591
Gross Unrealized Gains
Gross Unrealized Losses	(381)	(254)
Fair Value	29,058	19,337
Agency Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost	42,901	44,191
Gross Unrealized Gains		1
Gross Unrealized Losses	(1,156)	(831)
Fair Value	41,745	43,361
Mortgage-Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost	166,458	180,470
Gross Unrealized Gains	6	13
Gross Unrealized Losses	(7,625)	(5,868)
Fair Value	158,839	174,615
Corporate Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost	919,920	830,447
Gross Unrealized Gains	45	136
Gross Unrealized Losses	(27,117)	(13,790)
Fair Value	892,848	816,793
Municipal Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost	188,728	187,999
Gross Unrealized Gains	14	110
Gross Unrealized Losses	(3,157)	(2,004)
Fair Value	185,585	186,105
Other [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost	171,641	183,730
Gross Unrealized Gains	1	2
Gross Unrealized Losses	(2,787)	(2,223)
Fair Value	$ 168,855	$ 181,509

This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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