Annual report pursuant to Section 13 and 15(d)

Nature Of Operations And Accounting Policies Nature Of Operations And Accounting Policies (Schedule of Accumulated Other Comprehensive Income (Loss))(Details)

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Nature Of Operations And Accounting Policies Nature Of Operations And Accounting Policies (Schedule of Accumulated Other Comprehensive Income (Loss))(Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax $ (545) $ (11,593) $ (5,528) $ (3,494)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax, Portion Attributable to Parent 1,812 (9,331) (3,129)  
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax, Portion Attributable to Parent (795) 3,266 1,095  
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax 0 75 (116) (16)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, before Tax, Portion Attributable to Parent (260) 294 (154)  
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax, Portion Attributable to Parent 91 (103) 54  
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax 0 4 24 5
Other Comprehensive (Income) Loss, Defined Benefit Plan, before Tax, after Reclassification Adjustment, Attributable to Parent (6) (31) 29  
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax, Attributable to Parent 2 11 (10)  
Accumulated Other Comprehensive Income (Loss), Net of Tax (545) (11,514) (5,620) (3,505)
Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent 1,546 (9,068) (3,254)  
Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent (702) 3,174 1,139  
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax, Portion Attributable to Noncontrolling Interest 153 (1,085) (442)  
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax, Portion Attributable to Noncontrolling Interest 13 (17) 0  
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax, Portion Attributable to Noncontrolling Interest 0 0 0  
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax, Portion Attributable to Noncontrolling Interest 0 0 0  
Other Comprehensive (Income) Loss, Defined Benefit Plan, before Tax, after Reclassification Adjustment, Attributable to Noncontrolling Interest (5) (13) 13  
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax, Attributable to Noncontrolling Interest 0 0 0  
Other Comprehensive Loss, before Tax 1,707 (10,183) (3,683)  
Other Comprehensive Income (Loss), Tax (702) 3,174 1,139  
Other Comprehensive Income (Loss), Net of Tax 1,005 (7,009) (2,544)  
Non-Controlling Interests In Subsidiaries [Member]        
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax (1,460) (1,613) (528) (86)
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax (4) (17) 0 0
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax (2) 3 16 $ 3
Other Comprehensive Income (Loss), Net of Tax 161 $ (1,115) $ (429)  
SEACOR Marine Holdings Inc. [Member]        
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax, Portion Attributable to Parent 10,031      
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, before Tax, Portion Attributable to Parent 94      
Other Comprehensive (Income) Loss, Defined Benefit Plan, before Tax, after Reclassification Adjustment, Attributable to Parent 0      
Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent 10,125      
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax, Portion Attributable to Noncontrolling Interest 0      
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax, Portion Attributable to Noncontrolling Interest 0      
Other Comprehensive (Income) Loss, Defined Benefit Plan, before Tax, after Reclassification Adjustment, Attributable to Noncontrolling Interest $ 0