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Marketable Securities (Details) - USD ($)
$ in Thousands
Dec. 30, 2017
Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total $ 1,421,720 $ 1,480,237
U.S.Treasury Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 19,337 29,034
Agency Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 43,361 59,541
Mortgage-Backed Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 174,615 230,823
Corporate Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 816,793 893,725
Municipal Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 186,105 176,169
Other [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 181,509 90,945
Recurring Basis [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 1,421,720 1,480,237
Recurring Basis [Member] | U.S.Treasury Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 19,337 29,034
Recurring Basis [Member] | Agency Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 43,361 59,541
Recurring Basis [Member] | Mortgage-Backed Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 174,615 230,823
Recurring Basis [Member] | Corporate Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 816,793 893,725
Recurring Basis [Member] | Municipal Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 186,105 176,168
Recurring Basis [Member] | Other [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 181,509 90,946
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 1,421,720 1,480,237
Recurring Basis [Member] | Level 2 [Member] | U.S.Treasury Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 19,337 29,034
Recurring Basis [Member] | Level 2 [Member] | Agency Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 43,361 59,541
Recurring Basis [Member] | Level 2 [Member] | Mortgage-Backed Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 174,615 230,823
Recurring Basis [Member] | Level 2 [Member] | Corporate Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 816,793 893,725
Recurring Basis [Member] | Level 2 [Member] | Municipal Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 186,105 176,168
Recurring Basis [Member] | Level 2 [Member] | Other [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, total 181,509 90,946
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