v3.19.3.a.u2
Fair value of financial instruments - Conversion Option Derivative (Details) - Derivative Financial Instruments, Assets - Level 3
$ in Millions
12 Months Ended
Dec. 31, 2019
USD ($)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]  
Beginning balance of liability $ 1.2
Total unrealized loss 1.8
Currency transaction loss 0.2
Ending balance of liability $ 3.2