Fair Value Measurements - Summary of Categorization of Assets and Liabilities Measured at Fair Value (Parenthetical) (Detail) - Fair Value, Measurements, Nonrecurring [Member] - USD ($) $ in Thousands	Dec. 31, 2020	Sep. 30, 2020	Aug. 13, 2020	Jun. 16, 2020	May 04, 2020
Fair value of convertible notes	$ 170,191		$ 24,344	$ 145,847
Advisor Engine [Member]
Fair value of financial interest disposed off					$ 9,592
Thesys Group, Inc [Member]
Fair value of financial interest		$ 0