Quarterly report pursuant to Section 13 or 15(d)

Note 3 - Investments, at Equity, and Advances to 50% or Less Owned Companies (Details Textual)

v3.10.0.1
Note 3 - Investments, at Equity, and Advances to 50% or Less Owned Companies (Details Textual)
$ in Thousands
9 Months Ended
Sep. 28, 2018
USD ($)
Sep. 13, 2018
USD ($)
Jan. 17, 2018
USD ($)
Sep. 30, 2018
USD ($)
Sep. 30, 2017
USD ($)
Sep. 27, 2018
USD ($)
Payments to Acquire Property, Plant, and Equipment, Total       $ 37,763 $ 52,353  
Unrecorded Unconditional Purchase Obligation, Total       34,500    
Equity Method Investment, Other than Temporary Impairment       1,200    
Proceeds from Divestiture of Interest in Joint Venture       8,017  
Guarantor Obligations, Maximum Exposure, Undiscounted       46,100    
Grant DIS [Member]            
Capital Call       500    
SeaCosco Offshore LLC [Member]            
Number of Equipment Operated     8      
Payments to Acquire Property, Plant, and Equipment, Total     $ 161,100      
Equity Method Investment, Ownership Percentage     50.00%      
Partners' Capital Account, Contributions       27,000    
Unrecorded Unconditional Purchase Obligation, Total       5,300    
SEACOR Holdings [Member]            
Equity Method Investment, Other than Temporary Impairment       $ 1,200    
SEACOR Marlin LLC [Member]            
Equity Method Investment, Ownership, Percent Sold   51.00%        
Proceeds from Divestiture of Interest in Joint Venture   $ 8,000        
Gain (Loss) on Disposition of Business   $ 400        
OSV Partners [Member]            
Secured Long-term Debt, Noncurrent           $ 27,300
Investment in Affiliates, Amount of Preferred Equity Offereing Participated $ 5,000          
Payments to Acquire Interest in Subsidiaries and Affiliates, Total 1,100          
Commitment to Invest Additional Funds if Call By General Partner 1,100          
Payments to Acquire Loans Receivable 2,100          
OSV Partners [Member] | General Partner [Member]            
Partners' Capital Account, Contributions $ 5,000          
Other Offshore Marine Services Joint Ventures [Member]            
Equity Method Investment, Ownership Percentage       50.00%    
Guarantor Obligations, Maximum Exposure, Undiscounted       $ 500    
Allocable Share of Uncalled Capital       $ 1,000