Earnings per Share - EPS Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings Per Share [Abstract]
Net income	$ 12.7	$ 14.6	$ 30.0	$ 37.9
Less: Net income allocated to participating securities	(0.3)	(0.3)	(0.6)	(0.6)
Net income allocated to common shareholders	$ 12.4	$ 14.3	$ 29.4	$ 37.3
Weighted average number of common shares outstanding	18,447,053	18,138,754	18,365,939	18,461,063
Dilutive potential common shares outstanding:
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	255,075	183,697	293,199	194,609
Diluted weighted-average shares	18,702,128	18,322,451	18,659,138	18,655,672