Shareholders' Equity (Details 2) (USD $) In Thousands, except Per Share data, unless otherwise specified	1 Months Ended
	Apr. 30, 2012	Feb. 29, 2012
Series C
Shareholders' Equity
Cash distributions paid on preferred shares (in dollars per share)		$ 0.4453
Distribution paid or declared on preferred shares	$ 2,672	$ 2,672
Distributions on preferred stock declared (in dollars per share)	$ 0.4453
Series D
Shareholders' Equity
Cash distributions paid on preferred shares (in dollars per share)		$ 0.4063
Distribution paid or declared on preferred shares	6,167	6,167
Distributions on preferred stock declared (in dollars per share)	$ 0.4063
Series E
Shareholders' Equity
Cash distributions paid on preferred shares (in dollars per share)		$ 0.4531
Distribution paid or declared on preferred shares	4,984	4,984
Distributions on preferred stock declared (in dollars per share)	$ 0.4531
Common Stock
Shareholders' Equity
Cash distributions paid on common shares (in dollars per share)		$ 0.50
Distributions paid or declared on common shares	$ 41,900	$ 41,861
Distributions on common stock declared (in dollars per share)	$ 0.50