Annual report pursuant to Section 13 and 15(d)

Stock repurchase programs (Details)

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Stock repurchase programs (Details) (USD $)
0 Months Ended 12 Months Ended 1 Months Ended
Nov. 16, 2012
Sep. 30, 2012
Sep. 30, 2011
Sep. 30, 2010
Sep. 30, 2010
2008 and 2010 Plan
Nov. 30, 2011
2011 Plan
Stock Repurchase Programs            
Stock repurchase programs, authorized amount         $ 175,000,000 $ 125,000,000
Common shares repurchased 168,500 306,000 1,597,458 1,501,528    
Common shares repurchased, cost 9,700,000 12,796,000 57,484,000 40,217,000    
Amount remaining available for future stock repurchases   $ 127,400,000