Related Parties - Additional Information (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
	Oct. 26, 2015	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Related Party Transaction [Line Items]
Fees receivable		$ 519,496		$ 519,496		$ 537,442
Payments under tax receivable agreement				$ 25,454	$ 23,687
Amended and Restated Tax Receivable Agreement [Member]
Related Party Transaction [Line Items]
Tax agreement termination year				2033
Sponsored Funds [Member]
Related Party Transaction [Line Items]
Revenue		$ 118,573	$ 153,198	$ 254,528	$ 297,368
Type of Revenue [Extensible List]		us-gaap:AssetManagement1Member	us-gaap:AssetManagement1Member	us-gaap:AssetManagement1Member	us-gaap:AssetManagement1Member
Fees receivable		$ 49,189		$ 49,189		54,561
LTBP Trust [Member]
Related Party Transaction [Line Items]
Amount of cash savings in income or franchise tax that would be realized as a result of increases in tax basis and certain other tax benefits related to the amended and restated tax receivable agreement	45.00%
Cash tax saving that may arise from tax benefits attributable to payments under the amended and restated tax receivable agreement	85.00%
Cumulative liability relating to obligations under Amended and Restated Tax Receivable Agreement		$ 221,890		221,890		$ 247,344
Payments under tax receivable agreement				$ 25,454