Summary of significant accounting policies - Warrants (Details)	Jul. 28, 2015 shares
Series C Warrants Issued with Senior Debt \| Conversion of redeemable convertible preferred stock warrant into common stock warrant
Warrants
Warrants issued (in shares)	170,000
Common Stock Warrants \| Conversion of redeemable convertible preferred stock warrant into common stock warrant
Warrants
Warrants issued (in shares)	70,833
Common Stock \| Series C Warrants Issued with Series C Redeemable Preferred Stock Financing \| Cashless exercise of redeemable convertible preferred stock warrant into common stock
Warrants
Shares converted	947,185
Shares issued on conversion	78,926

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Number of securities into which the class of warrant or right may be converted. For example, but not limited to, 500,000 warrants may be converted into 1,000,000 shares.

+ References

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-Publisher FASB
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The number of shares converted in a noncash (or part noncash) transaction. Noncash is defined as transactions during a period that do not result in cash receipts or cash payments in the period. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

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The number of new shares issued in the conversion of stock in a noncash (or part noncash) transaction. Noncash is defined as transactions during a period that do not result in cash receipts or cash payments in the period. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

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