Goodwill and Other Intangible Assets - Gross Cost and Accumulated Amortization of Other Intangible Assets (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Other intangible assets, Gross Cost	$ 70,077	$ 69,706
Other intangible assets, accumulated amortization	67,973	65,949
Other intangible assets, Net Carrying Amount	2,104	3,757
Success/Incentive Fees [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangible assets, Gross Cost	35,295	35,232
Other intangible assets, accumulated amortization	33,547	32,235
Other intangible assets, Net Carrying Amount	1,748	2,997
Management Fees, Customer Relationships and Non-Compete Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangible assets, Gross Cost	34,782	34,474
Other intangible assets, accumulated amortization	34,426	33,714
Other intangible assets, Net Carrying Amount	$ 356	$ 760