Financial Highlights (Results Of Operations For A Share Outstanding) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Increase (Decrease) Earnings Per Share [Roll Forward]
Beginning Shareholders’ Equity Per Share (12/31/2011, 12/31/2010, and 12/31/2009, respectively)	$ 22.55	[1]	$ 24.47	[1]	$ 25.04
Net Investment Income	$ 1.35		$ 2.71		$ 1.91
Net Realized/Unrealized Gains (Losses)	$ 4.08		$ (2.08)		$ 1.22
Results of Operations (1)	$ 5.43	[2]	$ 0.63	[2]	$ 3.13	[2]
Dividends Paid	$ (2.50)		$ (2.51)		$ (2.45)
Weighted Average Share Impact on Dividends Paid (2)	$ (0.15)	[3]	$ (0.06)	[3]	$ (0.17)	[3]
Accretive (Dilutive) Effect of Share Issuances (Net of Offering Costs) and Share Repurchases	$ (0.47)		$ 0.02		$ (1.08)
Ending Shareholders’ Equity Per Share (12/31/2012, 12/31/2011, and 12/31/2010, respectively) (3)	$ 24.86	[1]	$ 22.55	[1]	$ 24.47	[1]
Shares Outstanding, end of period	20,370,469		16,447,651		16,498,342		11,972,113
Shareholders' equity per share upon conversion (in usd per share)	$ 24.38		$ 22.03		$ 23.91

[1] If all LTIP units previously issued were vested and exchanged for common shares as of December 31, 2012, 2011, and 2010, shareholders’ equity per share would be $24.38, $22.03, and $23.91, respectively.

[2] Calculated based on average common shares outstanding and can differ from the calculation for EPS (See Note 8).

[3] Per share impact on dividends paid relating to share issuances/repurchases during the period as well as dividends paid to LTIP unit holders.