Stockholders' Equity (Details 1) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Dividend Distributions
Total Dividend	$ 4,798	$ 4,947	$ 9,560	$ 9,874
Series F Preferred Stock [Member]
Dividend Distributions
Dividend/Distribution per Share			$ 2,811
Total Dividend			1,405
Series G Preferred Stock [Member]
Dividend Distributions
Dividend/Distribution per Share			$ 3,618
Total Dividend			905
Series J Preferred Stock [Member]
Dividend Distributions
Dividend/Distribution per Share			$ 9,063
Total Dividend			5,438
Series K Preferred Stock [Member]
Dividend Distributions
Dividend/Distribution per Share			$ 9,063
Total Dividend			$ 1,812