Details of Deferred Tax Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Current Deferred Tax Assets:
Step up in tax basis due to the exchange of LP Units for Class A Shares	$ 9,214	$ 8,621
Total Current Deferred Tax Asset	9,214	8,621
Long-term Deferred Tax Assets:
Depreciation and Amortization	14,673	13,180
Compensation and Benefits	25,958	23,002
Step up in tax basis due to the exchange of LP Units for Class A Shares	181,783	154,574
Other	17,043	15,859
Total Long-term Deferred Tax Assets	239,457	206,615
Long-term Deferred Tax Liabilities:
Goodwill and Investments	10,008	11,715
Total Long-term Deferred Tax Liabilities	10,008	11,715
Net Long-term Deferred Tax Assets Before Valuation Allowance	229,449	194,900
Valuation Allowance		(8,211)
Net Long-term Deferred Tax Assets	$ 229,449	$ 186,689