Consolidated Balance Sheet (Parenthetical) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Investments at value, cost	$ 1,634,790	$ 1,672,400
Financial derivatives–assets, at fair value Net cost	182,182	163,943
Repurchase agreements, cost	126,867	105,329
Investments sold short at value, proceeds	(708,403)	(731,048)
Financial derivatives-liabilities, at fair value Net proceeds	(51,443)	(56,200)
Securitized debt proceeds	$ (23,238)	$ 0
Common stock, par value
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	32,962,979	33,126,012
Common stock, shares outstanding	32,962,979	33,126,012