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Long-Term Debt and Capital Lease Obligations - Interest Expense (Details) - 2.125% cash convertible senior notes due 2019 [Member] - USD ($)
$ in Millions
12 Months Ended
Sep. 30, 2015
Sep. 30, 2014
Debt Instrument [Line Items]    
Interest expense $ 14.1 $ 3.5
Contractual interest expense 4.9 1.4
Debt discount amortization $ 9.2 $ 2.1
Effective interest rate 7.00% 7.00%
Remaining unamortized issuance discount period 4 years