Amortized Cost and Fair Value of Available for Sale Investments (Detail) - USD ($) $ in Thousands	Sep. 24, 2016	Dec. 26, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 109,265	$ 108,229
Gross Unrealized Gains	472	196
Gross Unrealized Losses	56	341
Fair Value	109,681	108,084
Money market investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,268	7,594
Fair Value	7,268	7,594
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,224	4,523
Gross Unrealized Gains	6	1
Gross Unrealized Losses	9	58
Fair Value	4,221	4,466
Corporate bonds and direct obligations of government agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	77,216	76,839
Gross Unrealized Gains	449	190
Gross Unrealized Losses	46	270
Fair Value	77,619	76,759
U.S. Treasury Obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	20,557	19,273
Gross Unrealized Gains	17	5
Gross Unrealized Losses	1	13
Fair Value	$ 20,573	$ 19,265

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=73527792&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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