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