Earnings per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Sep. 30, 2020
Earnings Per Share [Abstract]
Net Income (Loss) Attributable to Parent	$ 49,200,000	$ 93,900,000	$ 195,100,000	$ 180,600,000
Net income attributable to common shareholders per common share - Basic (usd per share)	$ 0.74	$ 1.41	$ 2.94	$ 2.71
Net income attributable to common shareholders per common share - Diluted (usd per share)	$ 0.74	$ 1.40	$ 2.92	$ 2.68
Average Common Shares Outstanding - Basic (in shares)	66,267	66,558	66,353	66,660
Add potential effect of exercise of stock options and other unvested equity awards (in shares)	574	625	516	632
Average shares outstanding - Diluted (in shares)	66,841	67,183	66,869	67,292
Shares with anti-dilutive effect excluded from the computation of Diluted EPS (in shares)	265		467	298	291