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, 2018
Sep. 30, 2017
Sep. 30, 2016
Summary of RSU activity      
Non-vested shares outstanding at the beginning of the period 822,827    
Granted (in shares) 365,071    
Vested (in shares) (464,658)    
Forfeited (in shares) (61,307)    
Non-vested shares outstanding at the end of the period 661,933 822,827  
Weighted-Average Grant-Date Fair Value      
Non-vested shares outstanding at the beginning of the period (in dollars per share) $ 51.69    
Granted (in dollars per share) 64.33 $ 53.63 $ 52.00
Vested (in dollars per share) 53.35    
Forfeited (in dollars per share) 54.90    
Non-vested shares outstanding at the end of the period (in dollars per share) $ 57.78 $ 51.69