Amortized Cost and Fair Value of Available for Sale Investments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 27, 2014	Dec. 28, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 103,058	$ 102,159
Gross Unrealized Gains	716	833
Gross Unrealized Losses	284	455
Fair Value	103,490	102,537
Money market investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,168	2,499
Fair Value	1,168	2,499
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,450	4,350
Gross Unrealized Gains	3	19
Gross Unrealized Losses	55	72
Fair Value	5,398	4,297
Corporate bonds and direct obligations of government agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	76,924	76,786
Gross Unrealized Gains	689	783
Gross Unrealized Losses	221	370
Fair Value	77,392	77,199
U.S. Treasury Obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	19,516	18,524
Gross Unrealized Gains	24	31
Gross Unrealized Losses	8	13
Fair Value	$ 19,532	$ 18,542