Shareholders' Equity - Narrative (Details) - USD ($)		3 Months Ended		6 Months Ended		9 Months Ended
	May 15, 2016	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Mar. 17, 2016	Sep. 14, 2015	Aug. 24, 2015
Class of Stock [Line Items]
Excess fair value of consideration paid over carrying value of preferred shares		$ 9,609,000	$ 0	$ 9,609,000	$ 0
Common Shares
Class of Stock [Line Items]
Stock repurchase program, authorized amount									$ 100,000,000.0
Stock repurchase program, additional authorized amount							$ 150,000,000	$ 100,000,000.0
Number of shares repurchased (in shares)				983,789		4,394,089
Treasury stock acquired, average cost per share (in USD per share)				$ 25.94		$ 25.80
Stock repurchased and retired during period, value				$ 25,500,000		$ 113,400,000
Remaining authorized repurchase amount		236,600,000		236,600,000		236,600,000
Remaining authorized repurchase amount, subject to expiration		$ 86,600,000		$ 86,600,000		$ 86,600,000
Series E
Class of Stock [Line Items]
Stock repurchased during period, shares	11,000,000
Redemption price per share (in USD per share)	$ 25.00
Preferred stock, redemption amount	$ 275,000,000