CONSOLIDATED STATEMENTS OF FINANCIAL CONDITION (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Financial instruments owned, at fair value, securities pledged	$ 324,146	$ 536,124
Common stock, shares authorized	1,000,000,000	1,000,000,000
Common stock, shares issued	106,025,000	127,508,000
Common stock, shares outstanding	90,156,000	116,860,000
Treasury stock, shares	15,869,000	10,649,000