Income Taxes (Taxability of Cash Distributions Paid on Common Shares) (Details) (Parent Company [Member], USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Parent Company [Member]
Investments, Owned, Federal Income Tax Note
Ordinary income (dollars per share)									$ 2.36	$ 2.16	$ 1.90
Ordinary income (percentage per share)									84.90%	81.64%	75.59%
Capital gains (dollars per share)									$ 0.17	$ 0.08	$ 0.10
Capital gains (percentage per share)									6.23%	3.09%	3.97%
Return of capital (dollars per share)									$ 0	$ 0	$ 0.28
Return of capital (percentage per share)									0.00%	0.00%	11.21%
Un-recaptured Section 1250 gain dividends per share									$ 0.25	$ 0.40	$ 0.23
Un-recaptured Section 1250 gain dividends per share percentage									8.87%	15.27%	9.23%
Total (dollars per share)	$ 0.6950	$ 0.6950	$ 0.6950	$ 0.6950	$ 0.6600	$ 0.6600	$ 0.6600	$ 0.6600	$ 2.78	$ 2.64	$ 2.51
Total (percentage per share)									100.00%	100.00%	100.00%