Earnings per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Net Income (Loss) Attributable to Parent	$ 49.5	$ 28.5	$ 91.7	$ 116.8
Average Common Shares Outstanding - Basic (in shares)	66,696	66,192	66,866	66,040
Add potential effect of exercise of stock options and other unvested equity awards (in shares)	648	1,405	659	1,468
Average shares outstanding - Diluted (in shares)	67,344	67,597	67,525	67,508
Net income attributable to common shareholders per common share - Basic (usd per share)	$ 0.74	$ 0.43	$ 1.37	$ 1.77
Net income attributable to common shareholders per common share - Diluted (usd per share)	$ 0.74	$ 0.42	$ 1.36	$ 1.73
Shares with anti-dilutive effect excluded from the computation of Diluted EPS (in shares)	307	280	286	225