Quarterly report pursuant to Section 13 or 15(d)

Revenue, Contract Assets and Liabilities and Other Contract Matters - Additional Information (Details)

v3.20.2
Revenue, Contract Assets and Liabilities and Other Contract Matters - Additional Information (Details)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2020
USD ($)
Jun. 30, 2019
USD ($)
Vechicle
Jun. 30, 2020
USD ($)
Vechicle
Jun. 30, 2019
USD ($)
Vechicle
Mar. 31, 2021
Dec. 31, 2020
Sep. 30, 2020
Dec. 31, 2019
USD ($)
Dec. 31, 2017
USD ($)
Long Term Contracts Or Programs Disclosure [Line Items]                  
Reduction of estimated contract price for liquidated damages, amount $ 11.6   $ 11.6         $ 12.9 $ 11.2
Retainage               $ 3.0  
Harbor Tug                  
Long Term Contracts Or Programs Disclosure [Line Items]                  
Change in estimated margins   $ 1.4 $ 0.6 $ 1.2          
Number of vehicle ferry projects | Vechicle     2            
Reserve for loss 0.6 $ 1.6 $ 0.6 $ 1.6          
Forty-Vehicle Ferry                  
Long Term Contracts Or Programs Disclosure [Line Items]                  
Change in estimated margins     $ 1.2            
Number of vehicle ferry projects | Vechicle   2 2 2          
Reserve for loss 2.5   $ 2.5            
Jacket and Deck                  
Long Term Contracts Or Programs Disclosure [Line Items]                  
Change in estimated margins 0.5   0.5            
Reserve for loss 0.1   0.1            
Paddlewheel Riverboat and Subsea Components Projects                  
Long Term Contracts Or Programs Disclosure [Line Items]                  
Change in estimated margins 0.5   1.4            
Ice-Breaker Tug                  
Long Term Contracts Or Programs Disclosure [Line Items]                  
Change in estimated margins   $ 0.9   $ 0.8          
Reserve for loss   0.1   0.1          
Forecast | Harbor Tug                  
Long Term Contracts Or Programs Disclosure [Line Items]                  
Projects, percent complete (percentage)           80.00% 93.00%    
Forecast | Forty-Vehicle Ferry                  
Long Term Contracts Or Programs Disclosure [Line Items]                  
Projects, percent complete (percentage)         60.00% 62.00%      
Forecast | Jacket and Deck                  
Long Term Contracts Or Programs Disclosure [Line Items]                  
Projects, percent complete (percentage)             94.00%    
Shipyard                  
Long Term Contracts Or Programs Disclosure [Line Items]                  
Change in estimated margins 0.6 $ 2.3 1.8 $ 2.0          
Fabrication & Services                  
Long Term Contracts Or Programs Disclosure [Line Items]                  
Change in estimated margins $ 1.0   $ 1.9