Fair value measurement - Valuation Technique (Details)	Dec. 31, 2018
Milestone-based payment | Discounted cash flow | Discount rate | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Business combination, contingent consideration, liability, measurement input	0.043
Milestone-based payment | Discounted cash flow | Discount rate | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Business combination, contingent consideration, liability, measurement input	0.062
Revenue-based | Discounted cash flow | Discount rate | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Business combination, contingent consideration, liability, measurement input	0.100
Revenue-based | Discounted cash flow | Discount rate | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Business combination, contingent consideration, liability, measurement input	0.105
Revenue-based | Monte Carlo simulation | Revenue volatility | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Business combination, contingent consideration, liability, measurement input	0.161
Revenue-based | Monte Carlo simulation | Revenue volatility | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Business combination, contingent consideration, liability, measurement input	0.250