Condensed Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2015	Dec. 31, 2014	[1]	Dec. 31, 2013	[1]
INVESTMENT INCOME
Interest income	$ 23,091	$ 26,440	$ 25,739	$ 26,513	$ 28,688		$ 22,353		$ 20,996		$ 21,496		$ 101,783	$ 93,533		$ 85,740
Other income	932	565	1,023	293	150		168		0		0		2,813	318		0
Total investment income	24,023	27,005	26,762	26,806	28,838		22,521		20,996		21,496		104,596	93,851		85,740
EXPENSES
Base management fee	2,772	2,849	2,920	2,952	2,963		3,056		2,368		2,364		11,493	10,751		9,115
Incentive fee					0		1,400		0		0		0	1,400		8,366
Interest expense	3,186	3,073	2,867	2,986	2,705		2,179		2,416		2,627		12,112	9,927		11,025
Other investment related expenses	1,774	1,473	1,163	1,202	1,810		1,217		1,232		430		5,612	4,689		496
Other operating expense	2,835	2,087	2,082	2,199	2,295		2,070		1,974		1,994
Total expenses	10,567	9,482	9,032	9,339	9,773		9,922		7,990		7,415		38,420	35,100		36,085
Net investment income	13,456	17,523	17,730	17,467	19,065		12,599		13,006		14,081		66,176	58,751		49,655
NET REALIZED AND CHANGE IN NET UNREALIZED GAIN (LOSS) ON INVESTMENTS, FINANCIAL DERIVATIVES, AND FOREIGN CURRENCY TRANSACTIONS/TRANSLATION
Net realized gain (loss) on investments, financial derivatives, and foreign currency transactions	1,483	8,280	761	10,429	(2,447)		(8,483)		3,684		11,408		20,953	4,162		18,002
Change in net unrealized gain (loss) on investments, financial derivatives, and foreign currency translation	(13,077)	(21,876)	(5,268)	(8,479)	(13,858)		9,031		4,514		(2,651)		(48,700)	(2,964)		11,705
Net Realized And Unrealized Gain Loss On Investments And Financial Derivatives, and foreign currency	(11,594)	(13,596)	(4,507)	1,950	(16,305)		548		8,198		8,757		(27,747)	1,198		29,707
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	1,862	3,927	13,223	19,417	2,760		13,147		21,204		22,838		38,429	59,949		79,362
Net Income (Loss) Attributable to Noncontrolling Interest	82	31	71	156	123		199		257		203		340	782		838
Net Income (Loss) Attributable to Parent	$ 1,780	$ 3,896	$ 13,152	$ 19,261	$ 2,637		$ 12,948		$ 20,947		$ 22,635		$ 38,089	$ 59,167		$ 78,524
NET INCREASE IN SHAREHOLDERS' EQUITY RESULTING FROM OPERATIONS PER SHARE:
Basic and Diluted (in usd per share)	$ 0.05	$ 0.12	$ 0.39	$ 0.57	$ 0.08	[2]	$ 0.46	[2]	$ 0.81	[2]	$ 0.88	[2]	$ 1.13	$ 2.09		$ 3.28

[1] Conformed to current period presentation.

[2] For the year ended December 31, 2014 the sum of EPS for the four quarters of the year does not equal EPS as calculated for the entire year (see Note 11) as a result of issuances of common shares and LTIP units during the year, as EPS is calculated using average shares outstanding during the period.