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Debt, net - Schedule of Debt - USD ($)
$ in Millions
Mar. 31, 2020
Sep. 30, 2019
Debt Instrument [Line Items]    
Debt $ 640.1 $ 460.5
Long-term Line of Credit 0.0 0.0
3.75% convertible senior notes due 2020, net of discount    
Debt Instrument [Line Items]    
Debt $ 0.0 116.7
Interest rate percentage 3.75%  
Senior Notes [Member]    
Debt Instrument [Line Items]    
Deferred finance costs, net $ 9.9 6.2
Senior Notes 8.0%    
Debt Instrument [Line Items]    
Debt $ 344.5 343.8
Interest rate percentage 8.00%  
Senior Notes 5.0%    
Debt Instrument [Line Items]    
Debt $ 295.6 $ 0.0
Interest rate percentage 5.00%