Goodwill and Other Intangible Assets - Gross Cost and Accumulated Amortization of Other Intangible Assets (Detail) - USD ($) $ in Thousands |
Dec. 31, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Finite-Lived Intangible Assets [Line Items] | ||
| Other intangible assets, Gross Cost | $ 69,706 | $ 69,171 |
| Other intangible assets, accumulated amortization | 65,949 | 63,099 |
| Other intangible assets, Net Carrying Amount | 3,757 | 6,072 |
| Success/Incentive Fees [Member] | ||
| Finite-Lived Intangible Assets [Line Items] | ||
| Other intangible assets, Gross Cost | 35,232 | 35,422 |
| Other intangible assets, accumulated amortization | 32,235 | 29,723 |
| Other intangible assets, Net Carrying Amount | 2,997 | 5,699 |
| Management Fees, Customer Relationships and Non-Compete Agreements [Member] | ||
| Finite-Lived Intangible Assets [Line Items] | ||
| Other intangible assets, Gross Cost | 34,474 | 33,749 |
| Other intangible assets, accumulated amortization | 33,714 | 33,376 |
| Other intangible assets, Net Carrying Amount | $ 760 | $ 373 |