Earnings per Share - EPS Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Earnings Per Share [Abstract]
Net income	$ 11.0	$ 14.5	$ 17.3	$ 23.3
Less: Net income allocated to participating securities	(0.2)	(0.3)	(0.3)	(0.4)
Net income allocated to common shareholders	$ 10.8	$ 14.2	$ 17.0	$ 22.9
Weighted average number of common shares outstanding	18,404,236	18,592,643	18,325,383	18,621,337
Dilutive potential common shares outstanding:
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	257,182	162,807	312,097	200,485
Diluted weighted-average shares	18,661,418	18,755,450	18,637,480	18,821,822