Consolidated Balance Sheet (Parenthetical) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Investments at value, cost	$ 1,883,248	$ 2,122,326
Financial derivatives–assets, at fair value Net cost	60,525	61,560
Repurchase agreements, cost	110,060	172,001
Investments sold short at value, proceeds	(985,360)	(1,290,091)
Financial derivatives-liabilities, at fair value Net proceeds	(48,316)	(33,555)
Securitized debt proceeds	$ (499)	$ (749)
Common stock, par value
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	33,417,118	33,449,678
Common stock, shares outstanding	33,417,118	33,449,678