Summary of Significant Accounting Policies Tax Characteristics of Dividends (Details)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Common Stock [Member]
Tax Characterization of Dividends Paid [Line Items]
Percent of Total Dividends Paid	100.00%	100.00%	100.00%
Preferred Stock [Member]
Tax Characterization of Dividends Paid [Line Items]
Percent of Total Dividends Paid	100.00%	100.00%	100.00%
Ordinary Income [Member] | Common Stock [Member]
Tax Characterization of Dividends Paid [Line Items]
Percent of Total Dividends Paid	3.30%	24.90%	69.00%
Ordinary Income [Member] | Preferred Stock [Member]
Tax Characterization of Dividends Paid [Line Items]
Percent of Total Dividends Paid	100.00%	57.00%	93.70%
Return of Capital [Member] | Common Stock [Member]
Tax Characterization of Dividends Paid [Line Items]
Percent of Total Dividends Paid	96.70%	56.30%	26.40%
Capital Gains [Member] | Common Stock [Member]
Tax Characterization of Dividends Paid [Line Items]
Percent of Total Dividends Paid	0.00%	18.80%	4.60%
Capital Gains [Member] | Preferred Stock [Member]
Tax Characterization of Dividends Paid [Line Items]
Percent of Total Dividends Paid	0.00%	43.00%	6.30%