Consolidated Balance Sheet (Parenthetical) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Investments at value, cost	$ 1,876,105	$ 1,525,710
Financial derivatives–assets, at fair value Net cost	37,658	40,724
Repurchase agreements, cost	294,468	185,205
Investments sold short at value, proceeds	782,395	589,429
Financial derivatives-liabilities, at fair value Net proceeds	16,024	12,012
Other secured borrowings proceeds	$ 61,802	$ 24,086
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	32,164,215	32,294,703
Common stock, shares outstanding	32,164,215	32,294,703