Accounting for derivative instruments and hedging activities - AOCI (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2020 |
Jun. 30, 2019 |
Jun. 30, 2020 |
Jun. 30, 2019 |
|
| AOCI Attributable to Parent, Net of Tax | ||||
| Change in fair value of cash flow hedges | $ (0.1) | $ 0.1 | $ (0.5) | $ 0.1 |
| Realized from OCI during the period | (0.1) | 0.2 | (0.2) | 0.3 |
| Interest rate swaps | ||||
| AOCI Attributable to Parent, Net of Tax | ||||
| Accumulated OCI balance at beginning of period | 1.3 | 1.5 | 1.6 | 1.6 |
| Change in fair value of cash flow hedges | (0.1) | 0.1 | (0.5) | 0.1 |
| Realized from OCI during the period | 0.1 | (0.2) | 0.2 | (0.3) |
| Accumulated OCI balance at end of period | $ 1.3 | $ 1.4 | $ 1.3 | $ 1.4 |