Annual report pursuant to Section 13 and 15(d)

Common Stock (Details)

v3.8.0.1
Common Stock (Details)
$ in Millions
12 Months Ended
Dec. 31, 2017
USD ($)
shares
Dec. 31, 2016
USD ($)
shares
Dec. 31, 2015
USD ($)
shares
Nov. 15, 2016
USD ($)
Equity, Class of Treasury Stock [Line Items]        
Treasury stock, shares acquired | shares     1,162,955  
Treasury Stock, Value, Acquired, Cost Method     $ 72.4  
Stock Repurchase Program, Authorized Amount       $ 150.0
Repurchase program, remaining authorized repurchase amount $ 77.4      
Restricted Stock        
Equity, Class of Treasury Stock [Line Items]        
Treasury stock, shares acquired | shares 212,659 47,455    
Treasury Stock, Value, Acquired, Cost Method $ 12.3 $ 2.4    
Employee Stock Option [Member]        
Equity, Class of Treasury Stock [Line Items]        
Treasury stock, shares acquired | shares     40,859  
Treasury Stock, Value, Acquired, Cost Method     $ 3.0  
Dorian LPG [Member]        
Equity, Class of Treasury Stock [Line Items]        
Common Stock Dividends, Shares | shares 3,977,135      
Dividends $ 31.4      
Stockholders' Equity Note, Stock Split, Conversion Ratio 0.2215