Earnings per Share - EPS Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Earnings Per Share [Abstract]
Net income	$ 14.6	$ 12.2	$ 37.9	$ 34.6
Less: Net income allocated to participating securities	(0.3)	(0.3)	(0.6)	(0.8)
Net income allocated to common shareholders	14.3	11.9	37.3	33.8
Diluted net income	14.6	12.2	37.9	34.6
Less: Diluted net income allocation to participating securities	(0.3)	(0.3)	(0.6)	(0.8)
Diluted net income allocated to common shareholders	$ 14.3	$ 11.9	$ 37.3	$ 33.8
Weighted average number of common shares outstanding	18,138,754	18,698,734	18,461,063	18,573,617
Dilutive potential common shares outstanding:
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	183,697	386,013	194,609	379,554
Diluted weighted-average shares	18,322,451	19,084,747	18,655,672	18,953,171