Consolidated Balance Sheet (Parenthetical) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Investments at value, cost	$ 1,799,464	$ 1,525,710
Financial derivatives–assets, at fair value Net cost	36,162	40,724
Repurchase agreements, cost	265,403	185,205
Investments sold short at value, proceeds	687,979	589,429
Financial derivatives-liabilities, at fair value Net proceeds	19,994	12,012
Other secured borrowings proceeds	$ 88,100	$ 24,086
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	32,112,694	32,294,703
Common stock, shares outstanding	32,112,697	32,294,703