Condensed Statements Of Financial Condition, Parent Company Only (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Condensed Financial Statements, Captions [Line Items]
Other Assets	$ 14,067	$ 11,718
Total Assets	1,145,218	1,043,592	898,085
LIABILITIES AND STOCKHOLDERS' EQUITY
Taxes Payable	20,304	5,159
Amounts Due Pursuant to Tax Receivable Agreement	165,350	137,448
Long-term Debt-Notes Payable	101,375	99,664
Total Liabilities	604,742	555,499
Additional Paid-In-Capital	654,275	575,122
Accumulated Other Comprehensive Income (Loss)	(9,086)	(12,058)
Retained Earnings (Deficit)	(77,079)	(76,703)
Treasury Stock at Cost (5,463,515 and 3,072,958 shares at December 31, 2012 and 2011, respectively)	(139,954)	(79,007)
TOTAL STOCKHOLDERS' EQUITY	428,506	407,664
Total Liabilities and Equity	1,145,218	1,043,592
Class A
LIABILITIES AND STOCKHOLDERS' EQUITY
Common Stock	350	310
Parent Company
Condensed Financial Statements, Captions [Line Items]
Equity Investment in Subsidiary	490,856	452,027
Deferred Tax Asset	225,741	188,256
Other Assets		14,310
Total Assets	716,597	654,593
LIABILITIES AND STOCKHOLDERS' EQUITY
Payable to Related Party	7,282	6,217
Taxes Payable	11,872
Amounts Due Pursuant to Tax Receivable Agreement	165,350	137,448
Long-term Debt-Notes Payable	101,375	99,664
Other Liabilities	2,212	3,600
Total Liabilities	288,091	246,929
Additional Paid-In-Capital	654,275	575,122
Accumulated Other Comprehensive Income (Loss)	(9,086)	(12,058)
Retained Earnings (Deficit)	(77,079)	(76,703)
Treasury Stock at Cost (5,463,515 and 3,072,958 shares at December 31, 2012 and 2011, respectively)	(139,954)	(79,007)
TOTAL STOCKHOLDERS' EQUITY	428,506	407,664
Total Liabilities and Equity	716,597	654,593
Parent Company | Class A
LIABILITIES AND STOCKHOLDERS' EQUITY
Common Stock	$ 350	$ 310