Earnings per Share - EPS Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015
Earnings Per Share [Abstract]
Net income	$ 14.5	$ 13.0	$ 23.3	$ 22.4
Less: Net income allocated to participating securities	(0.3)	(0.3)	(0.4)	(0.5)
Net income allocated to common shareholders	14.2	12.7	22.9	21.9
Diluted net income	14.5	13.0	23.3	22.4
Less: Diluted net income allocation to participating securities	(0.3)	(0.3)	(0.4)	(0.5)
Diluted net income allocated to common shareholders	$ 14.2	$ 12.7	$ 22.9	$ 21.9
Weighted average number of common shares outstanding	18,592,643	18,599,011	18,621,337	18,546,377
Dilutive potential common shares outstanding:
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	162,807	358,769	200,485	196,656
Diluted weighted-average shares	18,755,450	18,957,780	18,821,822	18,743,033