Condensed Quarterly Financial Data (Unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
INVESTMENT INCOME
Interest income	$ 28,688		$ 22,353	[1]	$ 20,996		$ 21,496		$ 22,954		$ 24,069		$ 20,335		$ 18,382		$ 93,533	$ 85,740	$ 63,857
Other investment income	150		168	[1]	0		0		0		0		0		0		318	0	0
Total investment income	28,838		22,521	[1]	20,996		21,496		22,954		24,069		20,335		18,382		93,851	85,740	63,857
EXPENSES
Base management fee	2,963		3,056	[1]	2,368		2,364		2,365		2,378		2,405		1,967		10,751	9,115	6,835
Incentive fee	0		1,400	[1]	0		0		3,091		2,038		1,182		2,055		1,400	8,366	19,145
Interest expense	2,705		2,179	[1]	2,416		2,627		3,024		3,277		2,582		2,142		9,927	11,025	7,799
Other investment related expenses	1,810		1,217	[1]	1,232		430		84		85		327		0		4,689	496	0
Other operating expenses	2,295		2,070	[1]	1,974		1,994		1,878		1,885		1,671		1,649
Total expenses	9,773		9,922	[1]	7,990		7,415		10,442		9,663		8,167		7,813		35,100	36,085	39,670
Net investment income	19,065		12,599	[1]	13,006		14,081		12,512		14,406		12,168		10,569		58,751	49,655	24,187
NET REALIZED AND UNREALIZED GAIN (LOSS) ON INVESTMENTS, FINANCIAL DERIVATIVES, AND FOREIGN CURRENCY TRANSACTIONS/TRANSLATION
Total net realized gain (loss) on investments, financial derivatives, and foreign currency transactions	(2,447)		(8,483)	[1]	3,684		11,408		(4,550)		4,289		5,671		12,592		4,162	18,002	(11,247)
Change in Net Unrealized Gain Loss On Investments, Financial derivatives, and Foreign currency translation	(13,858)		9,031	[1]	4,514		(2,651)		7,126		(6,872)		(6,134)		17,585		(2,964)	11,705	84,206
NET REALIZED AND UNREALIZED GAIN (LOSS) ON INVESTMENTS, FINANCIAL DERIVATIVES, AND FOREIGN CURRENCY TRANSACTIONS/TRANSLATION	(16,305)		548	[1]	8,198		8,757		2,576		(2,583)		(463)		30,177		1,198	29,707	72,959
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	2,760		13,147	[1]	21,204		22,838		15,088		11,823		11,705		40,746		59,949	79,362	97,146
Net Income (Loss) Attributable to Noncontrolling Interest	123		199	[1]	257		203		226		96		105		411		782	838	0
Net Income (Loss) Attributable to Parent	$ 2,637		$ 12,948	[1]	$ 20,947		$ 22,635		$ 14,862		$ 11,727		$ 11,600		$ 40,335		$ 59,167	$ 78,524	$ 97,146
NET INCREASE IN SHAREHOLDERS' EQUITY RESULTING FROM OPERATIONS PER SHARE:
Basic and Diluted (in usd per share)	$ 0.08	[2]	$ 0.46	[1],[2]	$ 0.81	[2]	$ 0.88	[2]	$ 0.58	[3]	$ 0.45	[3]	$ 0.49	[3]	$ 1.94	[3]	$ 2.09	$ 3.28	$ 5.31

[1] Prior period 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.

[3] For the year ended December 31, 2013 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.