Goodwill and Other Intangible Assets - Gross Cost and Accumulated Amortization of Other Intangible Assets (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Finite-Lived Intangible Assets [Line Items]
Other intangible assets, Gross Cost	$ 63,790	$ 63,803
Other intangible assets, Accumulated Amortization	51,754	45,379
Other intangible assets, Net Carrying Amount	12,036	18,424
Performance Fees [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangible assets, Gross Cost	30,740	30,740
Other intangible assets, Accumulated Amortization	21,116	17,173
Other intangible assets, Net Carrying Amount	9,624	13,567
Management Fees, Customer Relationships and Non-Compete Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangible assets, Gross Cost	33,050	33,063
Other intangible assets, Accumulated Amortization	30,638	28,206
Other intangible assets, Net Carrying Amount	$ 2,412	$ 4,857