Summary of Significant Accounting Policies Tax Characteristics of Dividends (Details)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
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	14.10%	3.30%	24.90%
Ordinary Income [Member] | Preferred Stock [Member]
Tax Characterization of Dividends Paid [Line Items]
Percent of Total Dividends Paid	100.00%	100.00%	57.00%
Return of Capital [Member] | Common Stock [Member]
Tax Characterization of Dividends Paid [Line Items]
Percent of Total Dividends Paid	85.90%	96.70%	56.30%
Capital Gains [Member] | Common Stock [Member]
Tax Characterization of Dividends Paid [Line Items]
Percent of Total Dividends Paid	0.00%	0.00%	18.80%
Capital Gains [Member] | Preferred Stock [Member]
Tax Characterization of Dividends Paid [Line Items]
Percent of Total Dividends Paid	0.00%	0.00%	43.00%