Goodwill - impairments (Details) - USD ($) $ in Millions |
12 Months Ended | |||
|---|---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2019 |
Dec. 31, 2018 |
Nov. 30, 2018 |
|
| Goodwill, Impaired [Abstract] | ||||
| Goodwill | $ 21.3 | $ 21.3 | $ 21.3 | |
| Amount of carrying value in excess of fair value | 0.0 | 0.0 | ||
| Curtis Palmer | ||||
| Goodwill, Impaired [Abstract] | ||||
| Goodwill | 14.4 | 14.4 | 14.4 | |
| Fair value in excess of carrying value | $ 8.3 | |||
| Fair value in excess of carrying value (as a percent) | 9.00% | |||
| Impairment of goodwill | 14.7 | |||
| Morris And Nipigon | ||||
| Goodwill, Impaired [Abstract] | ||||
| Fair value in excess of carrying value | $ 111.7 | |||
| Fair value in excess of carrying value (as a percent) | 118.00% | |||
| Impairment of goodwill | $ 0.0 | |||
| Morris | ||||
| Goodwill, Impaired [Abstract] | ||||
| Goodwill | 3.3 | 3.3 | 3.3 | |
| Nipigon | ||||
| Goodwill, Impaired [Abstract] | ||||
| Goodwill | $ 3.6 | $ 3.6 | $ 3.6 |