Contingent consideration Contingent consideration - Fair Value Level 3 of Significant Unobservable Inputs (Details) $ in Millions	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, measurement with unobservable inputs reconciliation, recurring basis, liability value	$ 29.1	$ 29.2
Discounted cash flow | Fair Value, Inputs, Level 3 | Fair Value, Recurring
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, measurement with unobservable inputs reconciliation, recurring basis, liability value	$ 29.1
Discounted cash flow | Fair Value, Inputs, Level 3 | Fair Value, Recurring | Discount rate | Minimum
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Business combination, contingent consideration, liability, measurement input	0.025
Discounted cash flow | Fair Value, Inputs, Level 3 | Fair Value, Recurring | Discount rate | Maximum
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Business combination, contingent consideration, liability, measurement input	0.086
Discounted cash flow | Fair Value, Inputs, Level 3 | Fair Value, Recurring | Discount rate | Weighted Average
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Business combination, contingent consideration, liability, measurement input	0.043
Discounted cash flow | Fair Value, Inputs, Level 3 | Fair Value, Recurring | Probability of payment | Minimum
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Business combination, contingent consideration, liability, measurement input	0.100
Discounted cash flow | Fair Value, Inputs, Level 3 | Fair Value, Recurring | Probability of payment | Maximum
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Business combination, contingent consideration, liability, measurement input	0.400
Discounted cash flow | Fair Value, Inputs, Level 3 | Fair Value, Recurring | Probability of payment | Weighted Average
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Business combination, contingent consideration, liability, measurement input	0.209