Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies Summary of Significant Accounting Policies - Derivative Financial Instruments (Details)

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Summary of Significant Accounting Policies Summary of Significant Accounting Policies - Derivative Financial Instruments (Details) - USD ($)
12 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Sep. 30, 2017
Sep. 25, 2019
Jul. 09, 2010
Derivative [Line Items]          
Accumulated other comprehensive income (loss) on derivative instruments, tax $ (300,000) $ (800,000)      
Other Nonoperating Income (Expense) 6,700,000 (200,000) $ 4,600,000    
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax (13,600,000) 900,000      
Cash Flow Hedging | Foreign Exchange Forward [Member]          
Derivative [Line Items]          
Derivative Instruments and Hedges, Assets 128,900,000 152,600,000      
Cash Flow Hedging | Interest Rate Swap [Member]          
Derivative [Line Items]          
Derivative Instruments and Hedges, Assets   50.0      
Derivative Instruments and Hedges, Liabilities 20.2        
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax $ 13,800,000        
Maximum          
Derivative [Line Items]          
Length of Time Hedged in Currency Exchange Rates 24 months        
2010 Notes          
Derivative [Line Items]          
Debt issued       $ 375,000,000.0  
$150 senior unsecured notes          
Derivative [Line Items]          
Debt issued         $ 150,000,000
Reclassification out of Accumulated Other Comprehensive Income          
Derivative [Line Items]          
Other Nonoperating Income (Expense) $ (8,200,000) (1,500,000) (5,100,000)    
Interest expense, interest rate swap amortization over next twelve months 2.0        
Reclassification out of Accumulated Other Comprehensive Income | Interest Rate Swap [Member]          
Derivative [Line Items]          
Other Nonoperating Income (Expense) (6.4)        
Net Unrealized Gain (Loss) on Derivative Instruments | Reclassification out of Accumulated Other Comprehensive Income          
Derivative [Line Items]          
Other Nonoperating Income (Expense) $ (6,500,000) $ 2,300,000 $ (100,000)