CONSOLIDATED STATEMENTS OF FINANCIAL CONDITION (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
CONSOLIDATED STATEMENTS OF FINANCIAL CONDITION
Financial instruments owned, at fair value, financial instruments pledged (in dollars)	$ 478,427	$ 1,095,431
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	133,769,219
Common stock, outstanding shares	122,942,752	124,440,655
Treasury stock, shares	10,826,427	9,328,564