Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Fair value measurements
Short-term investments	$ 0us-gaap_ShortTermInvestments	$ 11,511us-gaap_ShortTermInvestments
Recurring
Fair value measurements
Assets, fair value	19,011	17,843
Recurring \| Money market funds
Fair value measurements
Cash equivalents	19,011	6,332
Recurring \| Government securities
Fair value measurements
Short-term investments		11,511
Recurring \| Quoted prices in active markets for identical assets (Level 1)
Fair value measurements
Assets, fair value	19,011	6,332
Recurring \| Quoted prices in active markets for identical assets (Level 1) \| Money market funds
Fair value measurements
Cash equivalents	19,011	6,332
Recurring \| Quoted prices in active markets for identical assets (Level 1) \| Government securities
Fair value measurements
Short-term investments		0
Recurring \| Significant other observable inputs (Level 2)
Fair value measurements
Assets, fair value	0	11,511
Recurring \| Significant other observable inputs (Level 2) \| Money market funds
Fair value measurements
Cash equivalents	0	0
Recurring \| Significant other observable inputs (Level 2) \| Government securities
Fair value measurements
Short-term investments		11,511
Recurring \| Significant unobservable inputs (Level 3)
Fair value measurements
Assets, fair value	0	0
Recurring \| Significant unobservable inputs (Level 3) \| Money market funds
Fair value measurements
Cash equivalents	0	0
Recurring \| Significant unobservable inputs (Level 3) \| Government securities
Fair value measurements
Short-term investments		$ 0

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)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

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- Definition

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

-URI http://asc.fasb.org/extlink&oid=6507016

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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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