Schedule of Unrealized Loss on Available for Sale Investments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 28, 2015	Dec. 27, 2014
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments with unrealized losses, Less than 12 months, Fair Value	$ 8,359	$ 28,352
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	68	149
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value	9,941	14,580
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss	45	194
Available-for-sale investments with unrealized losses, Fair Value, Total	18,300	42,932
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	113	343
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments with unrealized losses, Less than 12 months, Fair Value	895	2,006
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	6	13
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value	2,468	2,447
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss	16	37
Available-for-sale investments with unrealized losses, Fair Value, Total	3,363	4,453
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	22	50
Corporate bonds and direct obligations of government agencies
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments with unrealized losses, Less than 12 months, Fair Value	2,561	19,354
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	59	135
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value	6,707	11,373
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss	28	149
Available-for-sale investments with unrealized losses, Fair Value, Total	9,268	30,727
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	87	284
U.S. Treasury Obligations
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments with unrealized losses, Less than 12 months, Fair Value	4,903	6,992
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	3	1
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value	766	760
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss	1	8
Available-for-sale investments with unrealized losses, Fair Value, Total	5,669	7,752
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	$ 4	$ 9

Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

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