Annual report pursuant to Section 13 and 15(d)

Savings Plans And Multiemployer Pension Plans (Details)

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Savings Plans And Multiemployer Pension Plans (Details) - USD ($)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets $ 38,492,000    
Defined Benefit Plan, Benefit Obligation (36,940,000)    
Defined Benefit Plan, Funded (Unfunded) Status of Plan 1,552,000    
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) $ 1,315,000    
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate 3.50%    
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase 4.50%    
Consumer Price Index 2.00%    
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Cash Balance Interest Credits 4.10%    
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets 6.75%    
Defined Benefit Plan, Expected Future Benefit Payment, Remainder of Fiscal Year $ 2,030    
Defined Benefit Plan, Expected Future Benefit Payment, Year Two 1,950    
Defined Benefit Plan, Expected Future Benefit Payment, Year Three 2,030    
Defined Benefit Plan, Expected Future Benefit Payment, Year Four 2,030    
Defined Benefit Plan, Expected Future Benefit Payment, Year Five 2,060    
Pension Plan      
Defined Benefit Plan Disclosure [Line Items]      
Pension and other postretirement benefit expense 2,400,000 $ 1,800,000 $ 1,500,000
Multiemployer Plans, Postretirement Benefit      
Defined Benefit Plan Disclosure [Line Items]      
Payment for Pension and Other Postretirement Benefits $ 1,000,000 300,000 200,000
Deferred Compensation Plan | SEACOR Deferred Compensation Plan      
Defined Benefit Plan Disclosure [Line Items]      
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent 75.00%    
Deferred compensation obligation $ 500,000 400,000  
Deferred Compensation Plan | SEACOR Deferred Compensation Plan | Deferred Bonus      
Defined Benefit Plan Disclosure [Line Items]      
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent 100.00%    
Deferred Compensation Plan | SEACOR Deferred Compensation Plan | Restricted Stock      
Defined Benefit Plan Disclosure [Line Items]      
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent 100.00%    
Domestic Plan [Member] | Savings Plan      
Defined Benefit Plan Disclosure [Line Items]      
Employer Matching Contribution Percent of Employees' Gross Pay 3.50%    
Defined Contribution Plan Contributions $ 1,800,000 $ 1,800,000 $ 3,800,000