Earnings per Common Share (Details) - USD ($)	3 Months Ended								12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Net income attributable to common shareholders	$ 27,900,000	$ 32,600,000	$ 49,500,000	$ 42,200,000	$ 90.4	$ 45.2	$ 28.5	$ 88.3	$ 152,200,000	$ 252,400,000	$ 133,600,000
Average shares outstanding - Basic (in shares)									66,772,000	66,234,000	65,599,000
Add potential effect of exercise of stock options and other unvested equity awards (in shares)									888,000	1,378,000	1,626,000
Average shares outstanding - Diluted (in shares)									67,660,000	67,612,000	67,225,000
Basic net income attributable to common shareholders per common share	$ 0.42	$ 490,000	$ 740,000	$ 630,000	$ 1.36	$ 0.68	$ 0.43	$ 1.34	$ 2.28	$ 3.81	$ 2.04
Diluted net income attributable to common shareholders per common share	$ 0.41	$ 480,000	$ 740,000	$ 620,000	$ 1.33	$ 0.67	$ 0.42	$ 1.31	$ 2.25	$ 3.73	$ 1.99
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount									288	263	20