Summary of Significant Accounting Policies Tax Characteristics of Dividends (Details)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
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%
Ordinary Income [Member] | Common Stock [Member]
Tax Characterization of Dividends Paid [Line Items]
Percent of Total Dividends Paid	4.20%	59.20%	52.60%
Ordinary Income [Member] | Preferred Stock [Member]
Tax Characterization of Dividends Paid [Line Items]
Percent of Total Dividends Paid		60.70%	55.00%
Return of Capital [Member] | Common Stock [Member]
Tax Characterization of Dividends Paid [Line Items]
Percent of Total Dividends Paid	0.00%	2.50%	4.40%
Capital Gains [Member] | Common Stock [Member]
Tax Characterization of Dividends Paid [Line Items]
Percent of Total Dividends Paid	95.80%	38.30%	43.00%
Capital Gains [Member] | Preferred Stock [Member]
Tax Characterization of Dividends Paid [Line Items]
Percent of Total Dividends Paid		39.30%	45.00%