Schedule of Unrealized Loss on Available for Sale Investments (Detail) - USD ($) $ in Thousands	Dec. 26, 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	$ 58,791	$ 28,352
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	288	149
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value	562	14,580
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss	53	194
Available-for-sale investments with unrealized losses, Fair Value, Total	59,353	42,932
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	341	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	4,422	2,006
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	58	13
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value		2,447
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss		37
Available-for-sale investments with unrealized losses, Fair Value, Total	4,422	4,453
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	58	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	39,276	19,354
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	217	135
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value	562	11,373
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss	53	149
Available-for-sale investments with unrealized losses, Fair Value, Total	39,838	30,727
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	270	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	15,093	6,992
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	13	1
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value		760
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss		8
Available-for-sale investments with unrealized losses, Fair Value, Total	15,093	7,752
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	$ 13	$ 9