Annual report pursuant to Section 13 and 15(d)

Equity - Summary of the Company's RSU Activity (Details)

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Equity - Summary of the Company's RSU Activity (Details) - Unvested restricted stock units - $ / shares
12 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2015
Summary of RSU activity      
Non-vested shares outstanding at the beginning of the period 809,306    
Granted (in shares) 448,289    
Vested (in shares) (400,583)    
Forfeited (in shares) (34,185)    
Non-vested shares outstanding at the end of the period 822,827 809,306  
Weighted-Average Grant-Date Fair Value      
Non-vested shares outstanding at the beginning of the period (in dollars per share) $ 47.64    
Granted (in dollars per share) 53.63 $ 52.00 $ 50.82
Vested (in dollars per share) 46.17    
Forfeited (in dollars per share) 46.00    
Non-vested shares outstanding at the end of the period (in dollars per share) $ 51.69 $ 47.64