Quarterly report pursuant to Section 13 or 15(d)

Subsequent Events - Additional Information (Details)

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