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Stock-Based Compensation, Other (Details) - Stock options - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended 6 Months Ended
Mar. 31, 2018
Dec. 31, 2017
Mar. 31, 2018
Stock based awards      
Weighted-average fair value of options granted (in dollars per share) $ 17.78 $ 12.94  
Total intrinsic value of options exercised (in dollars) $ 1.6   $ 5.6
Unrecognized compensation cost (in dollars) $ 11.8   $ 11.8
Period over which unrecognized compensation cost is expected to be recognized     2 years 2 months 12 days