CONSOLIDATED STATEMENTS OF FINANCIAL CONDITION (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
CONSOLIDATED STATEMENTS OF FINANCIAL CONDITION
Financial instruments owned, at fair value, financial instruments pledged (in dollars)	$ 1,553,610	$ 1,280,443
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	133,714,786	131,457,586
Common stock, outstanding shares	120,883,601	130,809,868
Treasury stock, shares	12,831,185	647,718