Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Earnings Per Share (Details)

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Summary of Significant Accounting Policies - Earnings Per Share (Details) - shares
3 Months Ended 12 Months Ended
Sep. 30, 2016
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Employee stock options granted (in shares) 0 300,000 750,000 0
Anti-dilutive equity awards (in shares)       0
Employee Stock Option        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Employee stock options granted (in shares)   300,000 750,000