Quarterly report pursuant to Section 13 or 15(d)

Long-Term Debt (Details)

v3.8.0.1
Long-Term Debt (Details) - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Debt Instrument [Line Items]      
Common Stock, par value $ 0.01   $ 0.01
Stock Repurchase Program, Remaining Authorized Repurchase Amount $ 77.4    
Letters of Credit Outstanding, Amount $ 11.1    
Seven Point Three Seven Five Percentage Senior Notes [Member]      
Debt Instrument [Line Items]      
Debt Instrument, Interest Rate, Stated Percentage 7.375%    
Three Point Zero Percentage Convertible Notes [Member]      
Debt Instrument [Line Items]      
Debt Instrument, Interest Rate, Stated Percentage 3.00%    
Two Point Five Percentage Convertible Notes [Member]      
Debt Instrument [Line Items]      
Debt Instrument, Interest Rate, Stated Percentage 2.50%    
Convertible Debt $ 64.5    
Other Debt Obligations [Member]      
Debt Instrument [Line Items]      
Repayments of long-term debt 0.2    
Sea-Vista [Member] | Revolving Credit Facility [Member]      
Debt Instrument [Line Items]      
Line of Credit Facility, Current Borrowing Capacity 55.0    
Sea-Vista [Member] | Term A-1 Loan [Member]      
Debt Instrument [Line Items]      
Repayments of long-term debt 0.8    
Sea-Vista [Member] | Term A-2 Loan [Member]      
Debt Instrument [Line Items]      
Repayments of long-term debt 1.4    
ISH [Member] | Revolving Credit Facility [Member]      
Debt Instrument [Line Items]      
Line of Credit Facility, Current Borrowing Capacity 5.0    
ISH [Member] | ISH Term Loan [Member]      
Debt Instrument [Line Items]      
Repayments of long-term debt 5.7    
SEACOR Marine Holdings Inc. [Member]      
Debt Instrument [Line Items]      
Letters of Credit Outstanding, Amount 0.7    
Guarantor Obligations, Maximum Exposure, Undiscounted 58.2    
Guaranty Fee Income $ 0.1 $ 0.2