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v3.21.1

Subsequent Events - Additional Information (Details) $ in Millions |  |  | 3 Months Ended | 12 Months Ended
--- | --- | --- | --- | ---
Apr. 19, 2021 USD ($) Vechicle drydock vessel Ship_project | Apr. 18, 2021 USD ($) | Jun. 30, 2021 USD ($) | Mar. 31, 2021 USD ($) | Mar. 31, 2021 USD ($) drydock | Dec. 31, 2020 USD ($) Vechicle drydock
Subsequent Event [Line Items] |  |  |  |  |  |
Number of drydocks | drydock |  |  |  |  | 2 |
Forty-Vehicle Ferry |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |
Number of vehicle ferry projects | Vechicle |  |  |  |  |  | 2
Shipyard Transaction |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |
Number of drydocks held for sale | drydock |  |  |  |  | 2 |
Estimated loss related to impairment of long lived assets and transaction costs |  |  |  |  | $ 23.4 |
Number of drydocks previously classified as held for sale | drydock |  |  |  |  |  | 2
Shipyard Transaction | Forecast |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |
Additional loss related to additional transaction and other costs |  |  | $ 2.0 |  |  |
Shipyard Transaction | Divested Shipyard Contracts |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |
Working capital liabilities |  |  |  | $ 10.4 | 10.4 | $ 11.2
Shipyard Transaction | Retained Shipyard Contracts And Other Shipyard Division Liabilities |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |
Working capital liabilities |  |  |  | 11.0 | $ 11.0 | $ 13.1
Subsequent Event | Shipyard Transaction |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |
Number of research vessels projects | vessel | 3 |  |  |  |  |
Number of divested shipyard contracts | Ship_project | 5 |  |  |  |  |
Number of drydocks | drydock | 4 |  |  |  |  |
Number of MPSV projects | vessel | 2 |  |  |  |  |
Pre tax loss on estimated carry value of net assets sold | $ 26.0 | $ 25.0 |  |  |  |
Subsequent Event | Shipyard Transaction | Forty-Vehicle Ferry |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |
Number of vehicle ferry projects | Vechicle | 2 |  |  |  |  |
Subsequent Event | Shipyard Transaction | Divested Shipyard Contracts |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |
Working capital liabilities | $ 11.2 |  |  |  |  |
Purchase Agreement | Bollinger | Shipyard Transaction |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |
Actual changes in working capital for divested shipyard contracts |  |  |  | $ 3.0 |  |
Purchase Agreement | Subsequent Event | Bollinger | Shipyard Transaction |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |
Transaction price | 28.6 |  |  |  |  |
Net of estimated transaction and other costs | 26.1 |  |  |  |  |
Transaction price on closing date | 26.4 |  |  |  |  |
Estimate change in working capital for divested shipyard contracts | $ 8.0 |  |  |  |  |
Mortgage Agreement and Restrictive Covenant Agreement | Subsequent Event | Shipyard Transaction | Seventy-Vehicle Ferry |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |
Number of vehicle ferry projects | Vechicle | 2 |  |  |  |  |

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