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Stock-Based Compensation, Other (Details) - Stock options - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Stock based awards    
Weighted-average fair value of options granted (in dollars per share) $ 12.94 $ 22.42
Total intrinsic value of options exercised (in dollars) $ 4.1 $ 11.6
Unrecognized compensation cost (in dollars) $ 13.7  
Period over which unrecognized compensation cost is expected to be recognized 3 years 4 months 24 days