Shareholders' Equity (Details 4) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Series D
Shareholders' Equity
Preferred shares outstanding	15,180,000	15,180,000
Preferred shares dividend (in dollars per share)	$ 1.625
Preferred shares, dividend yield (as a percent)	6.50%	6.50%
Liquidation preference (in dollars per share)	$ 25.00
Initial conversion rate	0.480775
Initial conversion price per share (in dollars per share)	$ 52.00
Additional common shares	7,298,165
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%
Purchase price as a percentage of liquidation preference	100.00%
Series E
Shareholders' Equity
Preferred shares outstanding	11,000,000	11,000,000
Preferred shares dividend (in dollars per share)	$ 1.8125
Preferred shares, dividend yield (as a percent)	7.25%	7.25%
Liquidation preference (in dollars per share)	$ 25.00
Redemption price per share (in dollars per share)	$ 25.00