Stockholders' Equity (Details 1) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Dividend Distributions
Total Dividend	$ 4,762	$ 4,927
Series F Preferred Stock [Member]
Dividend Distributions
Dividend/Distribution per Share	$ 1,369
Total Dividend	685
Series G Preferred Stock [Member]
Dividend Distributions
Dividend/Distribution per Share	$ 1,809
Total Dividend	452
Series J Preferred Stock [Member]
Dividend Distributions
Dividend/Distribution per Share	$ 4,531
Total Dividend	2,719
Series K Preferred Stock [Member]
Dividend Distributions
Dividend/Distribution per Share	$ 4,531
Total Dividend	$ 906