Shareholders' Equity - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions				3 Months Ended						9 Months Ended
	Jan. 27, 2020	Nov. 11, 2019	Apr. 29, 2019	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2020	Jun. 30, 2019	Jul. 31, 2015
Class of Stock [Line Items]
Common stock purchased (in shares)				980,136
Common stock purchased				$ 45.0	$ 45.0		$ 45.0
Average price (in dollars per share)				$ 45.93
Dividends to common shareholders				$ 20.8	$ 21.4	$ 21.4	$ 21.4	$ 21.6	$ 18.4
Dividend declared (in dollars per share)	$ (0.30)	$ (0.30)						$ (0.30)		$ (63,600,000)	$ (61,400,000)
Dividends paid on common stock										$ (64.3)	$ (61.7)
Preferred stock dividend declared (in dollars per share)	$ 1.875		$ 1.875
Payments of Ordinary Dividends, Preferred Stock and Preference Stock										$ 12.1	$ 4.0
Common Stock
Class of Stock [Line Items]
Number of shares authorized to be acquired (shares)												7,500,000
Common stock purchased (in shares)					980,000		1,036,000
Retained Earnings
Class of Stock [Line Items]
Dividends to common shareholders				$ 20.8	$ 21.4	$ 21.4	$ 21.4	$ 21.6	$ 18.4