Annual report pursuant to Section 13 and 15(d)

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

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Summary of Significant Accounting Policies - Derivative Financial Instruments (Details) - USD ($)
1 Months Ended 3 Months Ended 12 Months Ended
Sep. 30, 2019
Dec. 31, 2019
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2019
Sep. 25, 2019
Jul. 09, 2010
Derivative [Line Items]              
Accumulated other comprehensive income (loss) on derivative instruments, tax     $ (700,000) $ (700,000)      
Other     300,000 4,000,000.0 $ (6,700,000)    
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax     (10,200,000) (12,100,000)      
Carrying Value              
Derivative [Line Items]              
Derivative Asset     1,900,000 2,600,000      
Derivative Liability     2,500,000 1,600,000      
Cash Flow Hedging | Foreign Exchange Forward [Member]              
Derivative [Line Items]              
Derivative Instruments and Hedges, Assets     186,400,000 232,800,000      
Cash Flow Hedging | Interest Rate Swap [Member]              
Derivative [Line Items]              
Derivative Instruments and Hedges, Liabilities     20,200,000        
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        
Senior unsecured notes              
Derivative [Line Items]              
Debt issued     $ 375,000,000.0     $ 375,000,000.0  
Term of debt instrument 7 years            
$150.0 senior unsecured notes              
Derivative [Line Items]              
Debt issued             $ 150,000,000.0
Term of debt instrument   10 years          
Reclassification out of Accumulated Other Comprehensive Income              
Derivative [Line Items]              
Other     (2,000,000.0) 9,100,000 8,200,000    
Interest expense, interest rate swap amortization over next twelve months     2,000,000.0        
Reclassification out of Accumulated Other Comprehensive Income | Interest Rate Swap [Member]              
Derivative [Line Items]              
Other     6,400,000        
Net Unrealized Gain (Loss) on Derivative Instruments | Reclassification out of Accumulated Other Comprehensive Income              
Derivative [Line Items]              
Other     $ 1,900,000 $ 2,000,000.0 $ (6,500,000)