Annual report pursuant to Section 13 and 15(d)

Note 4 - Investments, at Equity, and Advances to 50% or Less Owned Companies - Equity Investments (Details)

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Note 4 - Investments, at Equity, and Advances to 50% or Less Owned Companies - Equity Investments (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Jan. 17, 2018
Investments at equity $ 121,773 $ 92,169    
MexMar [Member]        
Ownership percentage 49.00%      
Investments at equity $ 53,840 60,980    
Current assets 38,113 71,990    
Noncurrent assets 215,207 194,990    
Current liabilities 27,610 23,931    
Noncurrent liabilities 115,948 147,043    
Operating Revenues 57,003 67,003 $ 70,521  
Operating and administrative 25,932 29,405 37,613  
Depreciation 16,295 15,977 13,958  
42,227 45,382 51,571  
Operating Income 14,776 21,621 18,950  
Net Income 5,584 9,233 6,476  
All Other Excluding MexMar, Falcon Global, Sea-Cat Crewzer and Sea-Cat Crewzer II [Member]        
Current assets 61,287 61,360    
Noncurrent assets 352,421 247,038    
Current liabilities 32,302 14,603    
Noncurrent liabilities 209,752 138,789    
Operating Revenues 54,853 77,409 77,571  
Operating and administrative 53,967 46,748 51,136  
Depreciation 10,148 12,198 13,181  
64,115 58,946 64,317  
Operating Income (9,351) 18,463 (8,069)  
Net Income (20,383) 6,451 (19,229)  
Loss on Asset Dispositions and Impairments, Net $ (89) (21,323)  
SeaCosco Offshore LLC [Member]        
Ownership percentage 50.00%     50.00%
Investments at equity $ 28,002    
OSV Partners [Member]        
Ownership percentage 30.40%      
Investments at equity $ 11,087 10,006    
SEACOR Marlin LLC [Member]        
Ownership percentage 49.00%      
Investments at equity $ 7,579    
MEXMAR Offshore [Member]        
Ownership percentage 49.00%      
Investments at equity $ 4,900    
Offshore Vessel Holdings [Member]        
Ownership percentage 49.00%      
Investments at equity $ 4,900    
Dynamic Offshore [Member]        
Ownership percentage 19.00%      
Investments at equity $ 2,263 4,958    
Nautical Power [Member]        
Ownership percentage 50.00%      
Investments at equity 6,408    
Other Offshore Marine Services Joint Ventures [Member]        
Investments at equity $ 9,202 9,817    
Other Offshore Marine Services Joint Ventures [Member] | Minimum [Member]        
Ownership percentage 20.00%      
Other Offshore Marine Services Joint Ventures [Member] | Maximum [Member]        
Ownership percentage 50.00%      
Falcon Global, Sea-Cat Crewzer and Sea-Cat Crewzer II [Member]        
Operating Revenues   5,075 21,611  
Operating and administrative   3,752 12,837  
Depreciation   2,324 3,694  
  6,076 16,531  
Operating Income   (1,001) 5,080  
Net Income   $ (2,699) $ 778