Income taxes - Narrative (Details) - USD ($) |
12 Months Ended | |
---|---|---|
Dec. 31, 2015 |
Dec. 31, 2014 |
|
Income Taxes [Line Items] | ||
Increase (decrease) in valuation allowance | $ 9,900,000 | |
U.S. Federal | ||
Income Taxes [Line Items] | ||
Net operating loss carryforward | 28,200,000 | |
Research and development tax credit carryforwards | 500,000 | |
U.S. State | ||
Income Taxes [Line Items] | ||
Net operating loss carryforward | 24,100,000 | |
Research and development tax credit carryforwards | $ 200,000 | |
U.S. Federal and State | ||
Income Taxes [Line Items] | ||
Operating loss carryforwards that will increase additional paid in capital if used to reduce income taxes payable | $ 100,000 |