Condensed Quarterly Financial Data (Unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Quarterly Financial Information Disclosure [Abstract]
Interest income	$ 16,653	$ 15,426	$ 16,045	$ 15,733	$ 15,442	$ 15,597	$ 16,652	$ 15,849	$ 63,857	$ 63,540	$ 45,627
Base management fee	1,933	1,913	1,497	1,492	1,396	1,418	1,449	1,481	6,835	5,744	4,910
Incentive fee	7,342	9,491	2,312	0	0	0	0	612	19,145	612	4,428
Interest expense	2,039	1,936	1,992	1,832	1,874	1,627	1,603	1,543	7,799	6,647	3,826
Other operating expenses	1,666	1,354	1,422	1,449	1,126	1,575	1,526	1,615
Total expenses	12,980	14,694	7,223	4,773	4,396	4,620	4,578	5,251	39,670	18,845	20,840
NET INVESTMENT INCOME	3,673	732	8,822	10,960	11,046	10,977	12,074	10,598	24,187	44,695	24,787
Net realized gain (loss) on investments and financial derivatives	6,879	4,943	(11,280)	(11,789)	11,169	7,974	(3,916)	11,604	(11,247)	26,831	25,161
Change in net unrealized gain (loss) on investments and financial derivatives	14,234	23,862	13,226	32,884	(20,514)	(20,111)	(9,479)	(11,095)	84,206	(61,199)	(9,377)
NET REALIZED AND UNREALIZED GAIN (LOSS) ON INVESTMENTS AND FINANCIAL DERIVATIVES	21,113	28,805	1,946	21,095	(9,345)	(12,137)	(13,395)	509	72,959	(34,368)	15,784
Net increase in shareholders’ equity resulting from operations	$ 24,786	$ 29,537	$ 10,768	$ 32,055	$ 1,701	$ (1,160)	$ (1,321)	$ 11,107	$ 97,146	$ 10,327	$ 40,571
Basic and Diluted (in usd per share)	$ 1.19	$ 1.59	$ 0.64	$ 1.90	$ 0.10	$ (0.07)	$ (0.08)	$ 0.66	$ 5.31	$ 0.61	$ 3.04