Summary Of Significant Accounting Policies Schedule of Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes [Line Items]
Dividends Treatment For Federal Tax Purposes, Percentage	100.00%	100.00%	100.00%
Dividends treatment for federal tax purposes.	$ 2.37	$ 2.11	$ 2.00
Return of Capital [Member]
Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes [Line Items]
Dividends Treatment For Federal Tax Purposes, Percentage	0.00%	0.00%	41.61%
Dividends treatment for federal tax purposes.	$ 0.00	$ 0.00	$ 0.83
Capital Gains Income [Member]
Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes [Line Items]
Dividends Treatment For Federal Tax Purposes, Percentage	3.55%	2.61%	0.00%
Dividends treatment for federal tax purposes.	$ 0.08	$ 0.05	$ 0.00
Ordinary Income [Member]
Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes [Line Items]
Dividends Treatment For Federal Tax Purposes, Percentage	96.45%	97.39%	58.39%
Dividends treatment for federal tax purposes.	$ 2.29	$ 2.06	$ 1.17