Related Parties - Additional Information (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
	Oct. 26, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Related Party Transaction [Line Items]
Asset management fees		$ 301,719	$ 254,551	$ 868,522	$ 729,679
Fees receivable		451,218		451,218		$ 564,291
Payments under tax receivable agreement				789	10,086
Sponsored Funds [Member]
Related Party Transaction [Line Items]
Asset management fees		163,767	$ 130,546	471,727	$ 374,250
Fees receivable		57,156		57,156		49,944
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		$ 512,821		512,821		$ 513,610
Payments under tax receivable agreement				$ 789