Consolidated Statement Of Assets, Liabilities And Shareholders' Equity (Parenthetical) (USD $) In Thousands, except Share data	Sep. 30, 2011	Dec. 31, 2010
Consolidated Statement Of Assets, Liabilities And Shareholders' Equity [Abstract]
Investments at value, cost	$ 1,310,625	$ 1,232,484
Financial derivatives - assets, cost	119,307	208,958
Repurchase agreements, cost	18,035	25,684
Investments sold short at value, proceeds	562,607	775,782
Financial derivatives - liabilities, proceeds	$ 13,825	$ 17,718
Common stock, no par value
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	16,489,881	16,498,342
Common stock, shares outstanding	16,489,881	16,498,342