Goodwill and Other Intangible Assets - Gross Cost and Accumulated Amortization of Other Intangible Assets (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Intangible Assets [Line Items]
Other intangible assets, Gross Cost	$ 63,821	$ 63,775
Other intangible assets, Accumulated Amortization	38,039	35,281
Other intangible assets, Net Carrying Amount	25,782	28,494
Success\Performance Fees [Member]
Intangible Assets [Line Items]
Other intangible assets, Gross Cost	30,740	30,740
Other intangible assets, Accumulated Amortization	10,726	10,678
Other intangible assets, Net Carrying Amount	20,014	20,062
Management Fees, Customer Relationships and Non-Compete Agreements [Member]
Intangible Assets [Line Items]
Other intangible assets, Gross Cost	33,081	33,035
Other intangible assets, Accumulated Amortization	27,313	24,603
Other intangible assets, Net Carrying Amount	$ 5,768	$ 8,432