Income taxes (Credit Carryforwards Narrative) (Details) $ in Thousands	12 Months Ended
Dec. 31, 2016 USD ($)
Capital Loss Carryforward
Tax Credit Carryforward, Description	In addition to the tax benefits above, we have $310,000 of capital loss carryforwards that are scheduled to expire in 2017.
Tax Credit Carryforward, Amount	$ 310
Tax Credit Carryforward, Expiration Date	Dec. 31, 2017
R&D Tax Credit
Tax Credit Carryforward, Description	At December 31, 2016, we have net operating loss carryforwards of approximately $371.6 million for federal income tax reporting purposes. In addition, we have research and development tax credits of $7.0 million.
Tax Credit Carryforward, Amount	$ 7,000
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=65882285&loc=d3e32559-109319

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Carryforwards
-URI http://asc.fasb.org/extlink&oid=6506874

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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=65882285&loc=d3e32559-109319

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Carryforwards
-URI http://asc.fasb.org/extlink&oid=6506874

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

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