Condensed Consolidated Statements of Financial Condition (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Accounts Receivable, allowances	$ 2,149	$ 3,886
Furniture, Equipment and Leasehold Improvements, accumulated depreciation and amortization	24,139	19,880
Intangible Assets, accumulated amortization	$ 26,101	$ 20,002
Treasury Stock at Cost, shares	7,652,187	5,463,515
Class A [Member]
Common Stock, par value	$ 0.01	$ 0.01
Common Stock, shares authorized	1,000,000,000	1,000,000,000
Common Stock, shares issued	39,369,570	35,040,501
Common Stock, shares outstanding	31,717,383	29,576,986
Class B [Member]
Common Stock, par value	$ 0.01	$ 0.01
Common Stock, shares authorized	1,000,000	1,000,000
Common Stock, shares issued	42	43
Common Stock, shares outstanding	42	43