Goodwill and Other Intangible Assets - Gross Cost and Accumulated Amortization of Other Intangible Assets (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Intangible Assets [Line Items]
Other intangible assets, Gross Cost	$ 63,775	$ 63,364
Other intangible assets, Accumulated Amortization	35,281	26,922
Other intangible assets, Net Carrying Amount	28,494	36,442
Success/performance fees [Member]
Intangible Assets [Line Items]
Other intangible assets, Gross Cost	30,740	30,740
Other intangible assets, Accumulated Amortization	10,678	7,122
Other intangible assets, Net Carrying Amount	20,062	23,618
Management fees, customer relationships and non-compete agreements [Member]
Intangible Assets [Line Items]
Other intangible assets, Gross Cost	33,035	32,624
Other intangible assets, Accumulated Amortization	24,603	19,800
Other intangible assets, Net Carrying Amount	$ 8,432	$ 12,824