Summary of Short-Term Investments (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
Sep. 30, 2014	Dec. 31, 2013
Investment [Line Items]
Amortized cost	$ 84,140	$ 96,181
Unrealized Gains	9	42
Unrealized Losses	(42)	(25)
Estimated fair value	84,107	96,198
Corporate Debt Securities
Investment [Line Items]
Maturity	2 or less	2 or less
Amortized cost	68,270	71,402
Unrealized Gains	9	39
Unrealized Losses	(42)	(25)
Estimated fair value	68,237	71,416
Certificates of Deposit
Investment [Line Items]
Maturity	2 or less	2 or less
Amortized cost	13,870	11,710
Estimated fair value	13,870	11,710
Commercial Paper
Investment [Line Items]
Maturity	1 or less	1 or less
Amortized cost	2,000	6,069
Unrealized Gains		2
Estimated fair value	2,000	6,071
Debt securities of U.S. government-sponsored agencies
Investment [Line Items]
Maturity		1 or less
Amortized cost		7,000
Unrealized Gains		1
Estimated fair value		$ 7,001

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Maturity Period Of Short Term Investments

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No definition available.

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- Definition

This item represents the cost of Investments which are intended to be sold in the short term (usually less than one year or the normal operating cycle, whichever is longer) including trading securities, available-for-sale securities, held-to-maturity securities, and other short-term investments not otherwise listed in the existing taxonomy.

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No definition available.

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- Definition

Investments which are intended to be sold in the short term (usually less than one year or the normal operating cycle, whichever is longer) including trading securities, available-for-sale securities, held-to-maturity securities, and other short-term investments not otherwise listed in the existing taxonomy.

+ References

Reference 1: 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

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Subparagraph g

-Article 7

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- Definition

The increase (decrease), resulting in a gain, in the difference between the fair value and the carrying value, or in the comparative fair values, of securities held at each balance sheet date, that was included in earnings for the period.

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No definition available.

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- Definition

The increase (decrease), resulting in a loss, in the difference between the fair value and the carrying value, or in the comparative fair values, of securities held at each balance sheet date, that was included in earnings for the period.

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No definition available.

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