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Long-term Obligations - GMSL Credit Facility (Details) - USD ($)
1 Months Ended
Jan. 31, 2014
Dec. 31, 2016
Line of Credit Facility [Line Items]    
Outstanding debt   $ 388,702,000
Marine Services | Note Payable Collateralized by Assets    
Line of Credit Facility [Line Items]    
Basis spread on variable rate (as a percent) 3.65%  
Marine Services | Term Loan    
Line of Credit Facility [Line Items]    
Term loan amount established $ 20,000,000.0  
Marine Services | Term Loan | LIBOR    
Line of Credit Facility [Line Items]    
Debt instrument term 4 years 6 months