Payable to Employees and Related Parties (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Related Party Transaction [Line Items]
Board of Director Fees	$ 266		$ 235
Lexicon Deferred Consideration Payable			358
Amounts Due to Former Members of Lexicon	5,424		5,844
Amounts Due Pursuant to Tax Receivable Agreements	7,274	[1]	6,210	[1]
Payable to Employees and Related Parties	$ 12,964		$ 12,647

[1] Relates to the current portion of the Member exchange of LP Units for Class A Shares. The long-term portion of $165,350 and $137,448 is disclosed in Amounts Due Pursuant to Tax Receivable Agreements on the Consolidated Statements of Financial Condition at December 31, 2012 and 2011, respectively.