Fair value measurements (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
Jun. 30, 2015	Dec. 31, 2014
Fair value measurements
Short-term investments	$ 162	$ 0
Company's ending stock price (in dollars per share)	$ 0.35	$ 0.54
Company's stock volatility (as a percent)	85.00%	90.00%
Applicable risk free interest rate (as a percent)	1.40%	1.60%
Level 3 \| Warrants Liability Member
Fair value measurements
Beginning balance at January 1, 2015	$ 1,554
Change in estimated fair value	(867)
Ending balance at June 30, 2015	687	$ 1,554
Recurring \| Level 1
Fair value measurements
Assets	3,496	8,579
Cash and cash equivalents	3,291	8,579
Short-term investments	162
Trade accounts receivable	43
Liabilities	60	93
Recurring \| Level 1 \| KELTIP
Fair value measurements
KEL TIP liability	60	93
Recurring \| Level 3
Fair value measurements
Liabilities	687	1,554
Warrant liability	687	1,554
Recurring \| Fair Value
Fair value measurements
Assets	3,496	8,579
Cash and cash equivalents	3,291	8,579
Short-term investments	162
Trade accounts receivable	43
Liabilities	747	1,647
Warrant liability	687	1,554
Recurring \| Fair Value \| KELTIP
Fair value measurements
KEL TIP liability	60	93
Non-recurring \| Fair Value
Fair value measurements
Fair value measurements	$ 0	$ 0

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Fair value portion of amount due from customers or clients for goods or services, including trade receivables, that have been delivered or sold in the normal course of business, and amounts due from others, including related parties.

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- Definition

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

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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.

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-Publisher FASB

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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

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

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Amount of increase (decrease) 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.

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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.

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Fair value of asset after deduction of liability.

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Fair value of financial and nonfinancial obligations.

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Fair value portion of other liabilities.

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

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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.

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