Summary of Company Cash, Cash Equivalents and Short-term Investments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2015	Dec. 31, 2014
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	$ 166,240	$ 210,439
Cash, cash equivalents and short-term investments, Gross unrealized gains	0	0
Cash, cash equivalents and short-term investments, Gross unrealized losses	(17)	(95)
Cash, cash equivalents and short-term investments, Fair market value	166,223us-gaap_AvailableForSaleSecurities	210,344us-gaap_AvailableForSaleSecurities
Cash and Cash Equivalents [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	74,436	73,551
Cash, cash equivalents and short-term investments, Gross unrealized gains	0	0
Cash, cash equivalents and short-term investments, Fair market value	74,436	73,551
Short-term Investments [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	91,804	136,888
Cash, cash equivalents and short-term investments, Gross unrealized gains	0	0
Cash, cash equivalents and short-term investments, Gross unrealized losses	(17)	(95)
Cash, cash equivalents and short-term investments, Fair market value	91,787	136,793
Cash and Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	21,537	73,551
Cash, cash equivalents and short-term investments, Gross unrealized gains	0	0
Cash, cash equivalents and short-term investments, Fair market value	21,537	73,551
Commercial Paper [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	37,399	2,997
Cash, cash equivalents and short-term investments, Gross unrealized gains	0	0
Cash, cash equivalents and short-term investments, Gross unrealized losses	(1)
Cash, cash equivalents and short-term investments, Fair market value	37,398	2,997
US Government Debt Securities [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	77,232	75,289
Cash, cash equivalents and short-term investments, Gross unrealized gains	0	0
Cash, cash equivalents and short-term investments, Gross unrealized losses	(3)	(39)
Cash, cash equivalents and short-term investments, Fair market value	77,229	75,250
Corporate Bonds [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	30,072	58,602
Cash, cash equivalents and short-term investments, Gross unrealized gains	0	0
Cash, cash equivalents and short-term investments, Gross unrealized losses	(13)	(56)
Cash, cash equivalents and short-term investments, Fair market value	$ 30,059	$ 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

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

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+ References

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

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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

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

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