Annual report pursuant to Section 13 and 15(d)

Long-Term Debt (Narrative) (Senior Notes And Convertible Debentures) (Details)

v3.8.0.1
Long-Term Debt (Narrative) (Senior Notes And Convertible Debentures) (Details)
9 Months Ended 12 Months Ended
Sep. 30, 2017
USD ($)
Dec. 31, 2017
USD ($)
$ / shares
shares
Dec. 31, 2016
USD ($)
$ / shares
shares
Dec. 31, 2015
USD ($)
shares
Dec. 31, 2013
USD ($)
Dec. 31, 2012
USD ($)
Jul. 03, 2017
USD ($)
Nov. 15, 2016
USD ($)
Jun. 01, 2015
USD ($)
Apr. 15, 2015
USD ($)
Nov. 13, 2013
USD ($)
Dec. 11, 2012
USD ($)
Sep. 24, 2009
USD ($)
Debt Instrument [Line Items]                          
Common Stock, Par or Stated Value Per Share | $ / shares   $ 0.01 $ 0.01                    
Stock Repurchase Program, Authorized Amount               $ 150,000,000          
Convertible Securities | shares   5,258,065 0 0                  
Debt extinguishment gains (losses), net   $ (819,000) $ 5,184,000 $ (28,497,000)                  
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt   28,725,000 0 0                  
Letters of credit outstanding amount $ 27,200,000                        
Stock Repurchase Program, Remaining Authorized Repurchase Amount   77,400,000                      
Sea-Vista [Member]                          
Debt Instrument [Line Items]                          
Payments of Debt Issuance Costs       3,100,000                  
Debt extinguishment gains (losses), net   $ 700,000                      
Line of Credit Facility, Maximum Borrowing Capacity                   $ 300,000,000      
Sea-Vista [Member] | Minimum [Member]                          
Debt Instrument [Line Items]                          
Debt Instrument, Mandatory Prepayment Balance       75,000,000                  
Debt Instrument, Prepayment Increments       1,000,000                  
Sea-Vista [Member] | Minimum [Member] | London Interbank Offered Rate (LIBOR) [Member]                          
Debt Instrument [Line Items]                          
Debt Instrument, Basis Spread on Variable Rate   2.00%                      
Sea-Vista [Member] | Minimum [Member] | Base Rate [Member]                          
Debt Instrument [Line Items]                          
Debt Instrument, Basis Spread on Variable Rate   1.25%                      
Sea-Vista [Member] | Maximum [Member] | London Interbank Offered Rate (LIBOR) [Member]                          
Debt Instrument [Line Items]                          
Debt Instrument, Basis Spread on Variable Rate   2.75%                      
Sea-Vista [Member] | Maximum [Member] | Base Rate [Member]                          
Debt Instrument [Line Items]                          
Debt Instrument, Basis Spread on Variable Rate   1.75%                      
ISH [Member]                          
Debt Instrument [Line Items]                          
Payments of Debt Issuance Costs   $ 100,000                      
Line of Credit Facility, Maximum Borrowing Capacity             $ 25,000,000            
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage   0.50%                      
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt             28,700,000            
ISH [Member] | Minimum [Member]                          
Debt Instrument [Line Items]                          
Debt Instrument, Mandatory Prepayment Balance   $ 700,000                      
SEACOR Marine Holdings Inc. [Member]                          
Debt Instrument [Line Items]                          
Letters of credit outstanding amount   16,700,000                      
Guarantor Obligations, Maximum Exposure, Undiscounted   63,800,000                      
Guaranty Fee Income   $ 600,000 800,000                    
Three Point Zero Percentage Convertible Notes [Member]                          
Debt Instrument [Line Items]                          
Debt instrument, stated percentage   3.00%                 3.00%    
Aggregate principal amount                     $ 230,000,000    
Bond Trading Price Triggering Contingent Interest, Minimum         $ 1,200                
Individual Bond, Face Value                     $ 1,000    
Contingent Interest Rate                     0.45%    
Debt Instrument, Convertible, Conversion Ratio         12.5892                
Convertible Securities | shares   2,895,516                      
Bond Redemption Percentage   100.00%                      
Convertible Debt   $ 230,000,000 $ 230,000,000                    
Debt Instrument, Interest Rate, Effective Percentage     7.40%                    
Two Point Five Percentage Convertible Notes [Member]                          
Debt Instrument [Line Items]                          
Debt instrument, stated percentage   2.50% 2.50%                 2.50%  
Aggregate principal amount                       $ 350,000,000.0  
Bond Trading Price Triggering Contingent Interest, Minimum           $ 1,200              
Individual Bond, Face Value                       $ 1,000  
Contingent Interest Rate                       0.25%  
Debt Instrument, Convertible, Conversion Ratio   19.0381                      
Convertible Securities | shares   1,227,101                      
Bond Redemption Percentage   100.00%                      
Convertible Debt   $ 64,455,000 $ 157,128,000                    
Debt Instrument, Interest Rate, Effective Percentage   6.50%                      
Debt Instrument, Repurchased Face Amount   $ 61,700,000 127,400,000 65,500,000                  
Debt Instrument, Repurchase Amount   61,900,000 124,700,000 62,600,000                  
Debt extinguishment gains (losses), net   100,000 3,300,000 1,100,000                  
Two Point Five Percentage Convertible Notes [Member] | Additional Paid-In Capital [Member]                          
Debt Instrument [Line Items]                          
Debt Instrument, Repurchase Amount   1,400,000 7,400,000 3,000,000                  
7.375% Senior Notes [Member]                          
Debt Instrument [Line Items]                          
Debt instrument, stated percentage                         7.375%
Aggregate principal amount                         $ 250,000,000
Debt Instrument, Repurchased Face Amount   7,600,000 35,200,000 37,600,000                  
Debt Instrument, Repurchase Amount   7,700,000 33,100,000 37,900,000                  
Debt extinguishment gains (losses), net   (200,000) 1,900,000 600,000                  
Revolving Credit Facility [Member] | Sea-Vista [Member]                          
Debt Instrument [Line Items]                          
Debt Instrument, Unused Borrowing Capacity, Amount                   100,000,000      
Proceeds from Lines of Credit   44,900,000 87,000,000 30,000,000                  
Repayments of Lines of Credit   85,900,000 14,000,000 17,000,000                  
Line of Credit Facility, Current Borrowing Capacity   55,000,000                      
Revolving Credit Facility [Member] | ISH [Member]                          
Debt Instrument [Line Items]                          
Debt Instrument, Unused Borrowing Capacity, Amount             5,000,000            
Repayments of Long-term Debt 5,000,000                        
Line of Credit Facility, Current Borrowing Capacity   $ 5,000,000                      
Other ISH Debt [Member] | ISH [Member]                          
Debt Instrument [Line Items]                          
Debt instrument, stated percentage   7.00%                      
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt             3,900,000            
ISH Term Loan [Member] | ISH [Member]                          
Debt Instrument [Line Items]                          
Debt Instrument, Unused Borrowing Capacity, Amount             $ 20,000,000            
Repayments of Long-term Debt $ 7,800,000                        
Term A-1 Loan [Member] | Sea-Vista [Member]                          
Debt Instrument [Line Items]                          
Proceeds from issuance of long-term debt, net of offering costs       $ 80,000,000                  
Debt Instrument, Unused Borrowing Capacity, Amount                   80,000,000      
Debt Instrument, Periodic Payment, Principal, Percent       1.25%                  
Repayments of Long-term Debt   $ 39,400,000 3,800,000 $ 3,000,000                  
Term A-2 Loan [Member] | Sea-Vista [Member]                          
Debt Instrument [Line Items]                          
Proceeds from issuance of long-term debt, net of offering costs       $ 120,000,000                  
Debt Instrument, Unused Borrowing Capacity, Amount                   $ 120,000,000      
Debt Instrument, Periodic Payment, Principal, Percent       2.50%                  
Repayments of Long-term Debt   63,100,000                      
Title XI Bonds [Member]                          
Debt Instrument [Line Items]                          
Debt extinguishment gains (losses), net       $ 29,000,000                  
Repayments of Long-term Debt       99,900,000                  
Redemption Premium       20,500,000                  
Restricted Cash and Cash Equivalents                 $ 9,600,000        
Other Debt Obligations [Member]                          
Debt Instrument [Line Items]                          
Proceeds from issuance of long-term debt, net of offering costs     7,400,000 4,900,000                  
Repayments of Long-term Debt   $ 3,000,000 400,000 9,100,000                  
Other Debt Obligations [Member] | Minimum [Member]                          
Debt Instrument [Line Items]                          
Debt instrument, stated percentage   3.40%                      
Other Debt Obligations [Member] | Maximum [Member]                          
Debt Instrument [Line Items]                          
Debt instrument, stated percentage   4.30%                      
Long-term Debt [Member] | Two Point Five Percentage Convertible Notes [Member]                          
Debt Instrument [Line Items]                          
Debt Instrument, Repurchase Amount   $ 60,500,000 $ 117,300,000 $ 59,600,000                  
Put Option [Member] | Two Point Five Percentage Convertible Notes [Member]                          
Debt Instrument [Line Items]                          
Debt Instrument, Repurchased Face Amount   31,000,000                      
Debt Instrument, Repurchase Amount   $ 31,000,000