Income taxes (Credit Carryforwards Narrative) (Details) - R&D Tax Credit $ in Thousands	12 Months Ended
Dec. 31, 2017 USD ($)
Tax Credit Carryforward, Description	At December 31, 2017, we have net operating loss carryforwards of approximately $391.5 million for federal income tax reporting purposes. In addition, we have research and development tax credits of $7.4 million.
Tax Credit Carryforward, Amount	$ 7,400
Tax Credit Carryforward, Expiration Date	Dec. 31, 2018

The amount of the tax credit carryforward, before tax effects, available to reduce future taxable income under enacted tax laws.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32559-109319

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- Definition

A description of the origin, nature, and characteristics of the tax credit carryforward.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32559-109319

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Expiration date of the tax credit carryforward, in CCYY-MM-DD format.

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