Quarterly report pursuant to Section 13 or 15(d)

Supplemental disclosures (Details)

v3.8.0.1
Supplemental disclosures (Details) - USD ($)
shares in Thousands
 3 Months Ended 6 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Mar. 31, 2018
Mar. 31, 2017
Aug. 31, 2015
Payments for Repurchase of Equity [Abstract]          
Repurchases of common stock     $ 1,038,000 $ 28,858,000  
Restructuring Charges [Abstract]          
Restructuring charges $ 2,320,000        
Selling, general and administrative expense:          
Change in selling, general and administrative expenses 72,559,000 $ 68,596,000 $ 142,118,000 $ 133,994,000  
Restricted Stock Units (RSUs)          
Employee Benefits and Share-based Compensation, Noncash [Abstract]          
Granted (in shares)     300    
Vesting period     5 years    
Common Stock          
Payments for Repurchase of Equity [Abstract]          
Common shares repurchased     17 558  
United Kingdom          
Restructuring Charges [Abstract]          
Restructuring charges 2,300,000   $ 2,300,000 $ 2,200,000  
Mutual Fund          
Retirement Benefits [Abstract]          
Investments in mutual funds 16,300,000   16,300,000    
Estimated Revision Had Accounting Principle Been Adopted Previous Fiscal Year [Member]          
Selling, general and administrative expense:          
Change in selling, general and administrative expenses (1,300,000)   (2,500,000)    
Stock Repurchase Program, August 2015          
Payments for Repurchase of Equity [Abstract]          
Stock repurchase programs, authorized amount         $ 200,000,000
Amount remaining available for future stock repurchases $ 108,800,000   $ 108,800,000    
Stock Repurchase Program, August 2015 | Common Stock          
Payments for Repurchase of Equity [Abstract]          
Common shares repurchased     17 600  
Repurchases of common stock     $ 1,000,000 $ 28,900,000  
Board of Directors | Restricted Stock Units (RSUs)          
Employee Benefits and Share-based Compensation, Noncash [Abstract]          
Granted (in shares) 22        
Vesting period 1 year