Intangible Assets, Net - Summary of Intangible Assets, Net (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Definite-lived intangible assets:
Investment contracts	$ 425,747	$ 158,747
Accumulated amortization	(162,246)	(155,136)
Definite-lived intangible assets, net	263,501	3,611
Indefinite-lived intangible assets	43,516	34,816
Total intangible assets, net	$ 307,017	$ 38,427	$ 39,030	$ 40,887