Quarterly report pursuant to Section 13 or 15(d)

Supplemental disclosures (Details)

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Supplemental disclosures (Details) - USD ($)
 1 Months Ended 3 Months Ended
Nov. 30, 2015
Dec. 31, 2015
Dec. 31, 2014
Sep. 30, 2015
Aug. 31, 2015
Sep. 30, 2014
Income Taxes Paid, Net [Abstract]            
Income taxes paid   $ 19,150,000 $ 5,900,000      
Cash and Cash Equivalents [Abstract]            
Cash and cash equivalents   50,958,000 149,196,000 $ 74,672,000   $ 158,112,000
Foreign currency translation adjustments   (2,159,000) (10,480,000)      
Effect of exchange rate changes on cash and cash equivalents   590,000 3,606,000      
Decline in goodwill value   1,200,000        
Payments for Repurchase of Equity [Abstract]            
Stock repurchase programs, authorized amount         $ 200,000,000  
Repurchases of common stock   (29,139,000) $ (30,618,000)      
Amount remaining available for future stock repurchases   139,400,000.0        
Compensation and Retirement Disclosure [Abstract]            
Investments in mutual funds   $ 10,300,000        
Employee Benefits and Share-based Compensation [Abstract]            
Vesting period   5 years        
Restricted Stock Units (RSUs)            
Employee Benefits and Share-based Compensation [Abstract]            
Granted (in shares) 400,000.0          
Common Stock            
Payments for Repurchase of Equity [Abstract]            
Common shares repurchased   543,000 753,000      
Non-U.S.            
Cash and Cash Equivalents [Abstract]            
Cash and cash equivalents   $ 45,131,000