Schedule of Unrealized Loss on Available for Sale Investments (Detail) - USD ($) $ in Thousands	Mar. 26, 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	$ 34,700	$ 58,791
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	66	288
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value	6,296	562
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss	136	53
Available-for-sale investments with unrealized losses, Fair Value, Total	40,996	59,353
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	202	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	1,684	4,422
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	11	58
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value	2,428
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss	50
Available-for-sale investments with unrealized losses, Fair Value, Total	4,112	4,422
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	61	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	20,974	39,276
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	51	217
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value	3,868	562
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss	86	53
Available-for-sale investments with unrealized losses, Fair Value, Total	24,842	39,838
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	137	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	12,042	15,093
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	4	13
Available-for-sale investments with unrealized losses, Fair Value, Total	12,042	15,093
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	$ 4	$ 13