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Schedule of Unrealized Loss on Available-for-Sale Investments (Detail) - USD ($)
$ in Thousands
Jun. 30, 2018
Dec. 30, 2017
Debt Securities, Available-for-sale [Line Items]    
Available-for-sale investments with unrealized losses, Less than 12 months, Fair Value $ 80,603 $ 43,186
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss 1,144 224
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value 8,640 14,648
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss 175 116
Available-for-sale investments with unrealized losses, Fair Value, Total 89,243 57,834
Available-for-sale investments with unrealized losses, Unrealized Loss, Total 1,319 340
Asset-backed securities    
Debt Securities, Available-for-sale [Line Items]    
Available-for-sale investments with unrealized losses, Less than 12 months, Fair Value 1,199 1,864
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss 7 4
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value   632
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss   1
Available-for-sale investments with unrealized losses, Fair Value, Total 1,199 2,496
Available-for-sale investments with unrealized losses, Unrealized Loss, Total 7 5
Corporate bonds and direct obligations of government agencies    
Debt Securities, Available-for-sale [Line Items]    
Available-for-sale investments with unrealized losses, Less than 12 months, Fair Value 79,404 41,322
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss 1,137 220
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value 8,640 14,016
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss 175 115
Available-for-sale investments with unrealized losses, Fair Value, Total 88,044 55,338
Available-for-sale investments with unrealized losses, Unrealized Loss, Total $ 1,312 $ 335