Stockholders' and Mezzanine equity - Mezzanine Equity - Tabular Disclosure (Details) $ in Thousands	9 Months Ended
Sep. 30, 2017 USD ($)
Mezzanine equity
Mezzanine equity at the beginning of period	$ 88,975
Mezzanine equity at the end of period	89,413
Series A preferred stock
Mezzanine equity
Mezzanine equity at the beginning of period	88,975
Accretion on preferred stock	438
Mezzanine equity at the end of period	$ 89,413

Carrying amount, attributable to parent, of an entity's issued and outstanding stock which is not included within permanent equity. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. Includes stock with a put option held by an ESOP and stock redeemable by a holder only in the event of a change in control of the issuer.

No definition available.

Name:	us-gaap_TemporaryEquityCarryingAmountAttributableToParent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant