Fair value of financial instruments and marketable securities (Details 4) (Warrants, USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2015	Dec. 31, 2014
Changes in the fair value of warrant liability
Beginning balance	$ 188
Change in fair value of warrant liability	41
Ending balance	$ 229
Minimum
Assumption used to estimate the fair value of warrant liability by utilizing the Black-Scholes option-pricing model
Volatility (as a percent)	68.00%	68.00%
Risk-free interest rate (as a percent)	0.56%	0.89%
Strike price (in dollars per share)	$ 128	$ 128
Expected life	2 years 2 months 16 days	2 years 6 months
Maximum
Assumption used to estimate the fair value of warrant liability by utilizing the Black-Scholes option-pricing model
Volatility (as a percent)	70.00%	70.00%
Risk-free interest rate (as a percent)	1.13%	1.65%
Strike price (in dollars per share)	$ 2,520	$ 2,520
Expected life	4 years 5 months 23 days	4 years 8 months 12 days
Common stock
Assumption used to estimate the fair value of warrant liability by utilizing the Black-Scholes option-pricing model
Fair value of shares (in dollars per share)	$ 60.85	$ 51.77

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Agreed upon price for the exchange of the underlying asset.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (e)

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

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- Definition

Period the instrument, asset or liability is expected to be outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

+ Details

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- Definition

Measure of dispersion, in percentage terms (for instance, the standard deviation or variance), for a given stock price.

+ References

+ Details

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- Definition

Risk-free interest rate assumption used in valuing an instrument.

+ References

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- Definition

Amount of gain (loss) recognized on the income statement for financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)

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

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- Definition

Fair value of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)

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

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- Definition

Price of a single share of a number of saleable stocks of a company.

+ References

No definition available.

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