Schedule of Unrealized Loss on Available for Sale Investments (Detail) - USD ($) $ in Thousands	Jun. 25, 2016	Dec. 26, 2015
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments with unrealized losses, Less than 12 months, Fair Value	$ 5,326	$ 58,791
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	3	288
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value	3,940	562
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss	76	53
Available-for-sale investments with unrealized losses, Fair Value, Total	9,266	59,353
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	79	341
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments with unrealized losses, Less than 12 months, Fair Value		4,422
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss		58
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value	2,459
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss	15
Available-for-sale investments with unrealized losses, Fair Value, Total	2,459	4,422
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	15	58
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	5,326	39,276
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	3	217
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value	1,481	562
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss	61	53
Available-for-sale investments with unrealized losses, Fair Value, Total	6,807	39,838
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	$ 64	270
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		15,093
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss		13
Available-for-sale investments with unrealized losses, Fair Value, Total		15,093
Available-for-sale investments with unrealized losses, Unrealized Loss, Total		$ 13