Amortized Cost and Fair Value of Available for Sale Investments (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 27, 2014	Dec. 28, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 103,306	$ 102,159
Gross Unrealized Gains	506	833
Gross Unrealized Losses	343	455
Fair Value	103,469	102,537
Money market investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,729	2,499
Fair Value	1,729	2,499
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,106	4,350
Gross Unrealized Gains	1	19
Gross Unrealized Losses	50	72
Fair Value	5,057	4,297
Corporate bonds and direct obligations of government agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	76,964	76,786
Gross Unrealized Gains	491	783
Gross Unrealized Losses	284	370
Fair Value	77,171	77,199
U.S. Treasury Obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	19,507	18,524
Gross Unrealized Gains	14	31
Gross Unrealized Losses	9	13
Fair Value	$ 19,512	$ 18,542

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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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount of debt securities categorized neither as held-to-maturity nor trading.

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