Goodwill and Other Intangible Assets - Summary of Intangible Assets, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Definite-lived intangible assets, net:
Investment contracts	$ 425,747	$ 158,747
Accumulated amortization	(167,309)	(155,136)
Definite-lived intangible assets, net	258,438	3,611
Indefinite-lived intangible assets	43,516	34,816
Total intangible assets, net	$ 301,954	$ 38,427	$ 40,887	$ 41,783