Shareholders' Equity - Narrative (Details) - USD ($)		3 Months Ended		9 Months Ended		12 Months Ended
	Mar. 25, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Sep. 14, 2015	Aug. 24, 2015
Class of Stock [Line Items]
Distribution for the excess of the market value of common shares issued above carrying value of series D preferred shares redeemed		$ 0	$ 0	$ 0	$ 16,205,000
Common Shares
Class of Stock [Line Items]
Common shares issued to holders of preferred shares (in shares)				144		10,412,499
Stock repurchase program, authorized amount								$ 100,000,000.0
Stock repurchase program, additional authorized amount							$ 100,000,000.0
Number of shares repurchased (in shares)		3,410,300		3,410,300
Weighted average price per share of shares repurchased (in dollars per share)		$ 25.76		$ 25.76
Common shares from conversion of preferred shares (in shares)		2,363,103		2,363,103
Common Shares | Fundamental change conversion right
Class of Stock [Line Items]
Preferred shares converted into common shares (in shares)	10,411,779
Series D
Class of Stock [Line Items]
Preferred shares converted into common shares (in shares)				301		10,264,503
Liquidation preference (in dollars per share)	$ 25.00
Percentage of average closing market price of the entity's common stock based on which ratio for conversion of preferred shares into common shares is determined	98.00%
Number of consecutive trading days for calculating the average closing sale price of common shares	5 days
Common shares from conversion of preferred shares (in shares)		4,915,196		4,915,196
Series D | Fundamental change conversion right
Class of Stock [Line Items]
Preferred shares converted into common shares (in shares)	10,263,003
Distribution for the excess of the market value of common shares issued above carrying value of series D preferred shares redeemed	$ 16,200,000