Earnings per Share - EPS Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Net income	$ 24.0	$ 12.7	$ 39.8	$ 30.0
Less: Net income allocated to participating securities	(0.3)	(0.3)	(0.6)	(0.6)
Net income allocated to common shareholders	$ 23.7	$ 12.4	$ 39.2	$ 29.4
Weighted average number of common shares outstanding	18,597,165	18,447,053	18,524,846	18,365,939
Dilutive potential common shares outstanding:
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	379,733	255,075	351,413	293,199
Diluted weighted-average shares	18,976,898	18,702,128	18,876,259	18,659,138