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Marketable Securities (Details) - USD ($)
$ in Thousands
Mar. 31, 2018
Dec. 30, 2017
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total $ 1,476,930 $ 1,421,720
U.S.Treasury Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 29,058 19,337
Agency Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 41,745 43,361
Mortgage-Backed Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 158,839 174,615
Corporate Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 892,848 816,793
Municipal Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 185,585 186,105
Other [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 168,855 181,509
Recurring Basis [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 1,476,930 1,421,720
Recurring Basis [Member] | U.S.Treasury Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 29,058 19,337
Recurring Basis [Member] | Agency Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 41,744 43,361
Recurring Basis [Member] | Mortgage-Backed Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 158,839 174,615
Recurring Basis [Member] | Corporate Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 892,848 816,793
Recurring Basis [Member] | Municipal Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 185,586 186,105
Recurring Basis [Member] | Other [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 168,855 181,509
Recurring Basis [Member] | Level 1 [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total
Recurring Basis [Member] | Level 1 [Member] | U.S.Treasury Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total
Recurring Basis [Member] | Level 1 [Member] | Agency Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total
Recurring Basis [Member] | Level 1 [Member] | Mortgage-Backed Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total
Recurring Basis [Member] | Level 1 [Member] | Corporate Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total
Recurring Basis [Member] | Level 1 [Member] | Municipal Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total
Recurring Basis [Member] | Level 1 [Member] | Other [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total
Recurring Basis [Member] | Level 2 [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 1,476,930 1,421,720
Recurring Basis [Member] | Level 2 [Member] | U.S.Treasury Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 29,058 19,337
Recurring Basis [Member] | Level 2 [Member] | Agency Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 41,744 43,361
Recurring Basis [Member] | Level 2 [Member] | Mortgage-Backed Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 158,839 174,615
Recurring Basis [Member] | Level 2 [Member] | Corporate Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 892,848 816,793
Recurring Basis [Member] | Level 2 [Member] | Municipal Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 185,586 186,105
Recurring Basis [Member] | Level 2 [Member] | Other [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 168,855 181,509
Recurring Basis [Member] | Level 3 [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total
Recurring Basis [Member] | Level 3 [Member] | U.S.Treasury Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total
Recurring Basis [Member] | Level 3 [Member] | Agency Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total
Recurring Basis [Member] | Level 3 [Member] | Mortgage-Backed Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total
Recurring Basis [Member] | Level 3 [Member] | Corporate Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total
Recurring Basis [Member] | Level 3 [Member] | Municipal Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total
Recurring Basis [Member] | Level 3 [Member] | Other [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total