Financial Highlights (Results of Operations for a Share Outstanding) (Details) - $ / shares |
3 Months Ended | |||
|---|---|---|---|---|
Mar. 31, 2018 |
Mar. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
|
| Increase (Decrease) Equity Per Share [Roll Forward] | ||||
| Beginning Shareholders' Equity Per Share (12/31/2017) | $ 19.15 | |||
| Net Investment Income | 0.33 | |||
| Net Realized/Unrealized Gains (Losses) | 0.36 | |||
| Results of Operations Attributable to Equity | 0.69 | |||
| Less: Results of Operations Attributable to Non-controlling Interests | (0.01) | |||
| Results of Operations Attributable to Shareholders' Equity | 0.68 | |||
| Dividends Paid to Common Shareholders | (0.41) | |||
| Accretive (Dilutive) Effect of Share Issuances (Net of Offering Costs), Share Repurchases, and Adjustments to Non-controlling Interest | 0.14 | |||
| Ending Shareholders' Equity Per Share (3/31/2018 and 3/31/2017, respectively) | $ 19.56 | |||
| Shares Outstanding, end of period | 30,392,041 | 29,745,776 | 29,796,601 | 31,335,938 |
| Shareholders Equity Per Share Upon Conversion Of All Convertible Units (in usd per share) | $ 19.25 |