v3.10.0.1
Financial Highlights (Results Of Operations For A Share Outstanding) (Details) - $ / shares
 3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Mar. 31, 2018
Dec. 31, 2017
Mar. 31, 2017
Dec. 31, 2016
Increase (Decrease) Equity Per Share [Roll Forward]                
Beginning Shareholders' Equity Per Share (3/31/2018, 3/31/2017, 12/31/2017, and 12/31/2016, respectively) $ 19.56 $ 19.78 $ 19.15 $ 19.75        
Net Investment Income 0.36 0.26 0.70 0.63        
Net Realized/Unrealized Gains (Losses) 0.37 (0.09) 0.72 0.03        
Results of Operations Attributable to Equity 0.73 0.17 1.42 0.66        
Less: Results of Operations Attributable to Non-controlling Interests (0.03) (0.01) (0.04) (0.03)        
Results of Operations Attributable to Shareholders' Equity [1] 0.70 0.16 1.38 0.63        
Dividends Paid to Common Shareholders (0.41) (0.45) (0.82) (0.90)        
Weighted Average Share Impact on Dividends Paid [2] (0.01) (0.01) (0.02) (0.02)        
Accretive (Dilutive) Effect of Share Issuances (Net of Offering Costs), Share Repurchases, and Adjustments to Non-controlling Interest 0.05 0.01 0.20 0.03        
Ending Shareholders' Equity Per Share (3/31/2018 and 3/31/2017, respectively) [3] $ 19.89 $ 19.49 $ 19.89 $ 19.49        
Shares Outstanding, end of period 30,149,880 32,112,697 30,149,880 32,112,697 30,392,041 31,335,938 32,164,215 32,294,703
Shareholders Equity Per Share Upon Conversion Of All Convertible Units (in usd per share) $ 19.57 $ 19.21 $ 19.57 $ 19.21        
[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 June 30, 2018 and 2017, shareholders' equity per share would be $19.57 and $19.21, respectively.