Stockholders' equity (Details) - shares	Jun. 30, 2015	Dec. 31, 2014
Stockholders Equity Details
Options to purchase common stock	23,414
Options reserved for future issuance under the Company's 2007 Incentive Plan	78,887
Warrants to purchase common stock	8,380	26,769,000
Total reserved for future issuance	110,681