Summary of Company Cash, Cash Equivalents and Short-term Investments (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	$ 210,439	$ 256,965
Cash, cash equivalents and short-term investments, Gross unrealized gains	0	0
Cash, cash equivalents and short-term investments, Gross unrealized losses	(95)
Cash, cash equivalents and short-term investments, Fair market value	210,344us-gaap_AvailableForSaleSecurities	256,965us-gaap_AvailableForSaleSecurities
Cash and Cash Equivalents [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	73,551	256,965
Cash, cash equivalents and short-term investments, Gross unrealized gains	0	0
Cash, cash equivalents and short-term investments, Fair market value	73,551	256,965
Short-term Investments [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	136,888
Cash, cash equivalents and short-term investments, Gross unrealized gains	0
Cash, cash equivalents and short-term investments, Gross unrealized losses	(95)
Cash, cash equivalents and short-term investments, Fair market value	136,793
Cash and Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	73,551	256,965
Cash, cash equivalents and short-term investments, Gross unrealized gains	0	0
Cash, cash equivalents and short-term investments, Fair market value	73,551	256,965
Commercial Paper [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	2,997
Cash, cash equivalents and short-term investments, Gross unrealized gains	0
Cash, cash equivalents and short-term investments, Fair market value	2,997
Government and Government Agency Bonds [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	75,289
Cash, cash equivalents and short-term investments, Gross unrealized gains	0
Cash, cash equivalents and short-term investments, Gross unrealized losses	(39)
Cash, cash equivalents and short-term investments, Fair market value	75,250
Corporate Bonds [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	58,602
Cash, cash equivalents and short-term investments, Gross unrealized gains	0
Cash, cash equivalents and short-term investments, Gross unrealized losses	(56)
Cash, cash equivalents and short-term investments, Fair market value	$ 58,546

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 5

-Subparagraph (aa)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

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+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

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Amount of unrealized gain before deducting unrealized loss on investments in debt and equity securities classified as available-for-sale securities.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

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Amount of unrealized loss before deducting unrealized gain on investments in available-for-sale securities.

+ References

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

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-Name Accounting Standards Codification

-Topic 320

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