Summary of Significant Accounting Policies (Computation of Dividends Paid Deduction) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Accounting Policies [Abstract]
Cash dividends paid	$ 228,330	$ 232,203	$ 231,446
Less: Return of capital	(152,677)	(144,208)	(86,630)
Dividends Paid Deduction	75,653	87,995	144,816
Less: Capital gain distributions	0	0	(62,403)
Total dividends paid deduction attributable to adjusted taxable income	$ 75,653	$ 87,995	$ 82,413