Annual report pursuant to Section 13 and 15(d)

Nature Of Operations And Accounting Policies (Schedule Of Earnings Per Share) (Details)

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Nature Of Operations And Accounting Policies (Schedule Of Earnings Per Share) (Details) - USD ($)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Nov. 13, 2013
Dec. 11, 2012
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]          
Net Income (Loss) attributable to SEACOR Holdings Inc. $ 61,643,000 $ (215,897,000) $ (68,782,000)    
Dilutive Securities, Effect on Basic Earnings Per Share, Options and Restrictive Stock Units 0 0 0    
Dilutive Securities, Effect on Basic Earnings Per Share, Dilutive Convertible Securities 14,346,000 0 0    
Net Income (Loss) Available to Common Stockholders, Diluted $ 75,989,000 $ (215,897,000) $ (68,782,000)    
Average o/s Shares, Basic 17,368,081 16,914,928 17,446,137    
Incremental Common Shares Attributable to Share-based Payment Arrangements 308,012 0 0    
Convertible Securities 5,258,065 0 0    
Average o/s Shares, Diluted 22,934,158 16,914,928 17,446,137    
Basic Earnings (Loss) Per Common Share of SEACOR Holdings Inc. $ 3.55 $ (12.76) $ (3.94)    
Diluted Earnings (Loss) Per Common Share of SEACOR Holdings Inc. $ 3.31 $ (12.76) $ (3.94)    
Two Point Five Percentage Convertible Notes [Member]          
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]          
Convertible Securities 1,227,101        
Debt Instrument, Interest Rate, Stated Percentage 2.50% 2.50%     2.50%
Three Point Zero Percentage Convertible Notes [Member]          
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]          
Convertible Securities 2,895,516        
Debt Instrument, Interest Rate, Stated Percentage 3.00%     3.00%  
Stock Compensation Plan [Member]          
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]          
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount 1,924,217 2,020,677 2,078,777    
Convertible Debt Securities [Member] | Two Point Five Percentage Convertible Notes [Member]          
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]          
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount   2,664,208 4,148,327    
Convertible Debt Securities [Member] | Three Point Zero Percentage Convertible Notes [Member]          
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]          
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount   1,825,326 1,825,326