Accounting for derivative instruments and hedging activities - AOCI (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
|
| AOCI Attributable to Parent, Net of Tax | |||
| Change in fair value of cash flow hedges | $ (0.3) | $ 0.4 | $ (0.1) |
| Realized from OCI during the period | (0.3) | (0.1) | (0.5) |
| Interest rate swaps | |||
| AOCI Attributable to Parent, Net of Tax | |||
| Accumulated OCI balance at beginning of period | 1.6 | 1.1 | |
| Change in fair value of cash flow hedges | (0.3) | 0.4 | |
| Realized from OCI during the period | 0.3 | 0.1 | |
| Accumulated OCI balance at end of period | 1.6 | $ 1.6 | $ 1.1 |
| Settlements expected to be recognized from OCI in expense in the next 12 months, net of tax | 0.3 | ||
| Tax effect of gains (losses) expected to be realized from OCI in the next 12 months | $ 0.1 | ||