Amortized Cost and Fair Value of Available for Sale Investments (Detail) - USD ($) $ in Thousands	Dec. 26, 2015	Dec. 27, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 108,229	$ 103,306
Gross Unrealized Gains	196	506
Gross Unrealized Losses	341	343
Fair Value	108,084	103,469
Money market investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,594	1,729
Fair Value	7,594	1,729
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,523	5,106
Gross Unrealized Gains	1	1
Gross Unrealized Losses	58	50
Fair Value	4,466	5,057
Corporate bonds and direct obligations of government agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	76,839	76,964
Gross Unrealized Gains	190	491
Gross Unrealized Losses	270	284
Fair Value	76,759	77,171
U.S. Treasury Obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	19,273	19,507
Gross Unrealized Gains	5	14
Gross Unrealized Losses	13	9
Fair Value	$ 19,265	$ 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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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