Income Taxes - Uncertain tax positions (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
A reconciliation of the beginning and ending liability for uncertain tax positions
Balance at beginning of year	$ 336us-gaap_UnrecognizedTaxBenefits	$ 328us-gaap_UnrecognizedTaxBenefits
Increase Resulting from Current Period Tax Positions	248
Increases for tax position taken in prior years	8	8
Balance at the end of year	592us-gaap_UnrecognizedTaxBenefits	336us-gaap_UnrecognizedTaxBenefits
Unrecognized tax benefits that would affect the effective tax rate, if recognized	361
Accrued interest and penalties reported as income tax liability	$ 100	$ 70

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Amount of unrecognized tax benefits pertaining to uncertain tax positions taken in tax returns.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Unrecognized Tax Benefit

-URI http://asc.fasb.org/extlink&oid=6527854

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 15A

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Amount accrued for interest on an underpayment of income taxes and penalties related to a tax position claimed or expected to be claimed in the tax return.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 15

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32718-109319

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Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

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-Paragraph 15A

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Amount of increase in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

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The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 15A

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-URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319

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