CONSOLIDATED STATEMENTS OF FINANCIAL CONDITION (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
CONSOLIDATED STATEMENTS OF FINANCIAL CONDITION
Financial instruments owned, at fair value, financial instruments pledged (in dollars)	$ 1,099,916	$ 1,553,610
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, authorized shares	200,000,000	200,000,000
Common stock, issued shares	133,769,219	133,714,786
Common stock, outstanding shares	124,570,033	120,883,601
Treasury stock, shares	9,199,186	12,831,185