Revenue recognition - Performance Obligations (Details) - USD ($) $ in Millions |
Dec. 31, 2020 |
Dec. 31, 2019 |
---|---|---|
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01 | ||
Remaining Performance Obligation | ||
Deferred consideration payable | $ 11.7 | |
Revenue, performance obligation, period | 1 year | |
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01 | ||
Remaining Performance Obligation | ||
Deferred consideration payable | $ 4.2 | |
Revenue, performance obligation, period | 1 year |