Income Taxes (Distributions Paid) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Common Shares [Member]
Class of Stock [Line Items]
Ordinary Income Per Share	$ 1.1715	$ 0.9108	$ 0.6000
Qualified Dividend per Share	0.0213	0.0000	0.0000
Capital Gain Per Share	0.0000	0.0000	0.0000
Return of Capital Per Share	0.0000	0.0000	0.0000
Distributions Paid Per Share on a Tax Basis	$ 1.1928	$ 0.9108	$ 0.6000
Percentage of Ordinary Income	98.21%	100.00%	100.00%
Percentage of Qualified Dividend	1.79%	0.00%	0.00%
Percentage of Capital Gain	0.00%	0.00%	0.00%
Percentage of Return of Capital	0.00%	0.00%	0.00%
Percentage of Distributions Paid Per Share on a Tax Basis	100.00%	100.00%	100.00%
7.875% Series A [Member]
Class of Stock [Line Items]
Ordinary Income Per Share	$ 1.9336	$ 2.3948	$ 2.0349
Qualified Dividend per Share	0.0352	0.0000	0.0000
Capital Gain Per Share	0.0000	0.0000	0.0000
Return of Capital Per Share	0.0000	0.0000	0.0000
Distributions Paid Per Share on a Tax Basis	$ 1.9688	$ 2.3948	$ 2.0349
Percentage of Ordinary Income	98.21%	100.00%	100.00%
Percentage of Qualified Dividend	1.79%	0.00%	0.00%
Percentage of Capital Gain	0.00%	0.00%	0.00%
Percentage of Return of Capital	0.00%	0.00%	0.00%
Percentage of Distributions Paid Per Share on a Tax Basis	100.00%	100.00%	100.00%
8.00% Series B [Member]
Class of Stock [Line Items]
Ordinary Income Per Share	$ 1.9643	$ 2.4328	$ 2.0672
Qualified Dividend per Share	0.0357	0.0000	0.0000
Capital Gain Per Share	0.0000	0.0000	0.0000
Return of Capital Per Share	0.0000	0.0000	0.0000
Distributions Paid Per Share on a Tax Basis	$ 2.0000	$ 2.4328	$ 2.0672
Percentage of Ordinary Income	98.21%	100.00%	100.00%
Percentage of Qualified Dividend	1.79%	0.00%	0.00%
Percentage of Capital Gain	0.00%	0.00%	0.00%
Percentage of Return of Capital	0.00%	0.00%	0.00%
Percentage of Distributions Paid Per Share on a Tax Basis	100.00%	100.00%	100.00%
6.50% Series C [Member]
Class of Stock [Line Items]
Ordinary Income Per Share	$ 1.5960	$ 1.9767	$ 0.9890
Qualified Dividend per Share	0.0290	0.0000	0.0000
Capital Gain Per Share	0.0000	0.0000	0.0000
Return of Capital Per Share	0.0000	0.0000	0.0000
Distributions Paid Per Share on a Tax Basis	$ 1.6250	$ 1.9767	$ 0.9890
Percentage of Ordinary Income	98.22%	100.00%	100.00%
Percentage of Qualified Dividend	1.78%	0.00%	0.00%
Percentage of Capital Gain	0.00%	0.00%	0.00%
Percentage of Return of Capital	0.00%	0.00%	0.00%
Percentage of Distributions Paid Per Share on a Tax Basis	100.00%	100.00%	100.00%