Amortized Cost and Fair Value of Available for Sale Investments (Detail) - USD ($) $ in Thousands	Sep. 26, 2015	Dec. 27, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 108,040	$ 103,306
Gross Unrealized Gains	382	506
Gross Unrealized Losses	111	343
Fair Value	108,311	103,469
Money market investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	9,754	1,729
Fair Value	9,754	1,729
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,856	5,106
Gross Unrealized Gains		1
Gross Unrealized Losses	17	50
Fair Value	4,839	5,057
Corporate bonds and direct obligations of government agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	73,783	76,964
Gross Unrealized Gains	372	491
Gross Unrealized Losses	93	284
Fair Value	74,062	77,171
U.S. Treasury Obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	19,647	19,507
Gross Unrealized Gains	10	14
Gross Unrealized Losses	1	9
Fair Value	$ 19,656	$ 19,512

This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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