Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Short-term investments:
Total short-term investments	$ 16,646us-gaap_ShortTermInvestments	$ 13,263us-gaap_ShortTermInvestments
Restricted cash—money market fund	250	250
Recurring basis [Member]
Cash equivalents:
Total cash equivalents	8,451	10,364
Short-term investments:
Total short-term investments	16,646	13,263
Restricted cash—money market fund	250	250
Total assets measured at fair value	25,347	23,877
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Recurring basis [Member]
Cash equivalents:
Total cash equivalents	8,451	9,362
Short-term investments:
Restricted cash—money market fund	250	250
Total assets measured at fair value	8,701	9,612
Direct or Indirect Observable Inputs (Level 2) [Member] \| Recurring basis [Member]
Cash equivalents:
Total cash equivalents		1,002
Short-term investments:
Total short-term investments	16,646	13,263
Total assets measured at fair value	16,646	14,265
Corporate debt securities [Member]
Short-term investments:
Total short-term investments	15,447	12,713
Corporate debt securities [Member] \| Recurring basis [Member]
Cash equivalents:
Total cash equivalents		1,002
Short-term investments:
Total short-term investments	15,447	12,713
Corporate debt securities [Member] \| Direct or Indirect Observable Inputs (Level 2) [Member] \| Recurring basis [Member]
Cash equivalents:
Total cash equivalents		1,002
Short-term investments:
Total short-term investments	15,447	12,713
Corporate commercial paper [Member]
Short-term investments:
Total short-term investments	1,199	550
Corporate commercial paper [Member] \| Recurring basis [Member]
Short-term investments:
Total short-term investments	1,199	550
Corporate commercial paper [Member] \| Direct or Indirect Observable Inputs (Level 2) [Member] \| Recurring basis [Member]
Short-term investments:
Total short-term investments	1,199	550
Money market funds [Member] \| Recurring basis [Member]
Cash equivalents:
Total cash equivalents	8,451	9,362
Money market funds [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Recurring basis [Member]
Cash equivalents:
Total cash equivalents	$ 8,451	$ 9,362

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash

-URI http://asc.fasb.org/extlink&oid=6506951

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash Equivalents

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- Definition

Cash and equivalents whose use in whole or in part is restricted for the long-term, generally by contractual agreements or regulatory requirements.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 1

-Article 5

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 210.5-02.1)

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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

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-Name Regulation S-X (SX)

-Number 210

-Section 03

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-Article 7

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