Information Regarding Short-Term and Long-Term Marketable Securities (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Schedule of Held-to-maturity Securities [Line Items]
Marketable securities, Amortized Cost	$ 84,572	$ 62,102
Marketable securities, Unrealized Gains	55	26
Marketable securities, Unrealized Losses	(61)	(31)
Marketable securities, Fair Value	84,566	62,097
U.S. government agency securities
Schedule of Held-to-maturity Securities [Line Items]
Marketable securities, Amortized Cost	23,714	23,011
Marketable securities, Unrealized Gains	8	2
Marketable securities, Unrealized Losses	(5)	(4)
Marketable securities, Fair Value	23,717	23,009
Corporate debt securities
Schedule of Held-to-maturity Securities [Line Items]
Marketable securities, Amortized Cost	23,767	14,675
Marketable securities, Unrealized Gains	29	18
Marketable securities, Unrealized Losses	(28)	(14)
Marketable securities, Fair Value	23,768	14,679
Commercial paper
Schedule of Held-to-maturity Securities [Line Items]
Marketable securities, Amortized Cost	5,493	1,500
Marketable securities, Unrealized Losses	(13)
Marketable securities, Fair Value	5,480	1,500
U.S. municipal securities
Schedule of Held-to-maturity Securities [Line Items]
Marketable securities, Amortized Cost	26,901	17,971
Marketable securities, Unrealized Gains	10	3
Marketable securities, Unrealized Losses	(14)	(12)
Marketable securities, Fair Value	26,897	17,962
Certificates of deposit/time deposits
Schedule of Held-to-maturity Securities [Line Items]
Marketable securities, Amortized Cost	4,697	4,945
Marketable securities, Unrealized Gains	8	3
Marketable securities, Unrealized Losses	(1)	(1)
Marketable securities, Fair Value	$ 4,704	$ 4,947

For an unclassified balance sheet, this item represents investments in debt securities which are categorized as held-to-maturity. The held-to-maturity category is for those securities that the entity has the positive intent and ability to hold until maturity.

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

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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Reference 5: http://www.xbrl.org/2003/role/presentationRef

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Reference 6: http://www.xbrl.org/2003/role/presentationRef

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 9: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 10: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Accounting Research Bulletin (ARB)

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-Section A

-Paragraph 4

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 11: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 7

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 12: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

- Definition

This item represents the aggregate fair value of investments in debt securities as of the balance sheet date and which are categorized as held-to-maturity.

+ References+ Details

- Definition

As of the balance sheet date, the excess of fair value over carrying value (amortized cost) of a debt security categorized as held-to-maturity, exclusive of dividend or interest income recognized but not yet received and exclusive of any write-downs for other-than-temporary impairment. Such item represents the gross unrecognized holding gain.

+ References+ Details

- Definition

As of the balance sheet date, the excess of carrying value (amortized cost) over fair value of a debt security categorized as held-to-maturity, exclusive of dividend or interest income recognized but not yet received and exclusive of any write-downs for other-than-temporary impairment. Such item represents the gross unrecognized holding loss.

+ References+ Details