Financial Highlights (Results Of Operations For A Share Outstanding) (Details) - $ / shares		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Increase (Decrease) Equity Per Share [Roll Forward]
Beginning Shareholders' Equity Per Share (12/31/2017 and 12/31/2016, respectively)		$ 19.15	$ 19.75
Net Investment Income		0.33	0.37
Net Realized/Unrealized Gains (Losses)		0.36	0.11
Results of Operations Attributable to Equity		0.69	0.48
Less: Results of Operations Attributable to Non-controlling Interests		(0.01)	(0.01)
Results of Operations Attributable to Shareholders' Equity	[1]	0.68	0.47
Dividends Paid to Common Shareholders		(0.41)	(0.45)
Weighted Average Share Impact on Dividends Paid	[2]	(0.00)	(0.01)
Accretive (Dilutive) Effect of Share Issuances (Net of Offering Costs), Share Repurchases, and Adjustments to Non-controlling Interest		0.14	0.02
Ending Shareholders' Equity Per Share (3/31/2018 and 3/31/2017, respectively)	[3]	$ 19.56	$ 19.78
Shares Outstanding, end of period		30,392,041	32,164,215	31,335,938	32,294,703
Shareholders Equity Per Share Upon Conversion Of All Convertible Units (in usd per share)		$ 19.25	$ 19.50

[1] Calculated based on average common shares outstanding and can differ from the calculation for EPS (See Note 13).

[2] Per share impact on dividends paid relating to share issuances/repurchases during the period as well as dividends paid to LTIP and OP Unit holders.

[3] If all LTIP Units and OP Units previously issued were vested and exchanged for common shares as of March 31, 2018 and 2017, shareholders' equity per share would be $19.25 and $19.50, respectively.