Schedule of Unrealized Loss on Available for Sale Investments (Detail) - USD ($) $ in Thousands	Sep. 24, 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	$ 19,446	$ 58,791
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	25	288
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value	3,789	562
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss	31	53
Available-for-sale investments with unrealized losses, Fair Value, Total	23,235	59,353
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	56	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	1,482	4,422
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	1	58
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value	2,395
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss	8
Available-for-sale investments with unrealized losses, Fair Value, Total	3,877	4,422
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	9	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	13,947	39,276
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	23	217
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value	1,394	562
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss	23	53
Available-for-sale investments with unrealized losses, Fair Value, Total	15,341	39,838
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	46	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	4,017	15,093
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	1	13
Available-for-sale investments with unrealized losses, Fair Value, Total	4,017	15,093
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	$ 1	$ 13