Intangible Assets, Net - Summary of Intangible Assets, Net (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Definite-lived intangible assets:
Investment contracts	$ 425,747	$ 425,747
Accumulated amortization	(172,345)	(167,309)
Definite-lived intangible assets, net	253,402	258,438
Indefinite-lived intangible assets	43,516	43,516
Total intangible assets, net	$ 296,918	$ 301,954	$ 38,194	$ 38,427