Consolidated Statement Of Assets, Liabilities And Shareholders' Equity (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Statement of Financial Position [Abstract]
Investments at value, cost	$ 1,328,153	$ 1,234,203
Financial derivatives - assets, cost	65,860	118,281
Repurchase agreements, cost	13,650	15,750
Investments sold short at value, proceeds	621,048	459,013
Financial derivatives - liabilities, proceeds	13,171	9,636
Securitized debt proceeds	$ 1,311	$ 0
Common stock, par value
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	20,370,469	16,447,651
Common stock, shares outstanding	20,370,469	16,447,651