Fair value of financial instruments - Derivative liability (Details) - Recurring basis - Level 3 $ in Thousands	Dec. 31, 2019 USD ($) Y	Oct. 02, 2019 USD ($) Y	Dec. 31, 2018 USD ($) Y
Encina
Methodologies and significant inputs used in the determination of the fair value
Valuation Method	us-gaap:ValuationTechniqueDiscountedCashFlowMember	us-gaap:ValuationTechniqueDiscountedCashFlowMember
Fair value of liability at valuation date | $	$ 66	$ 69
Encina | Time period from valuation until end of earnout (in years)
Methodologies and significant inputs used in the determination of the fair value
Derivative Liability | Y	2.4	2.6
Encina | Cumulative probability of a change in control prepayment implied by model (in percent)
Methodologies and significant inputs used in the determination of the fair value
Derivative Liability	23.9	24.7
Encina | Discount rate (in percent)
Methodologies and significant inputs used in the determination of the fair value
Derivative Liability	6.00	6.00
Deerfield
Methodologies and significant inputs used in the determination of the fair value
Valuation Method	us-gaap:ValuationTechniqueOptionPricingModelMember		us-gaap:ValuationTechniqueOptionPricingModelMember
Fair value of liability at valuation date | $	$ 1,069		$ 2,017
Deerfield | Time period from valuation until end of earnout (in years)
Methodologies and significant inputs used in the determination of the fair value
Derivative Liability | Y	2.4		3.4
Deerfield | Cumulative probability of a change in control prepayment implied by model (in percent)
Methodologies and significant inputs used in the determination of the fair value
Derivative Liability	23		25.10
Deerfield | Cumulative probability of other accelerated prepayments implied by model (in percent)
Methodologies and significant inputs used in the determination of the fair value
Derivative Liability	10		13.70
Deerfield | Discount rate (in percent)
Methodologies and significant inputs used in the determination of the fair value
Derivative Liability	25.34		23.12