Goodwill and Other Intangible Assets - Intangible Assets Other Than Goodwill (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 417,583	$ 488,727
Accumulated amortization	(114,904)	(218,016)
Net	302,679	270,711
Indefinite-lived Intangible Assets [Line Items]
Gross carrying amount	437,083	508,227
Accumulated amortization	(114,904)	(218,016)
Net	322,179	290,211
Trade name
Indefinite-lived Intangible Assets [Line Items]
Gross carrying amount	$ 19,500	19,500
Financial professional relationships
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life	181 months
Gross carrying amount	$ 318,700	318,700
Accumulated amortization	(92,436)	(71,066)
Net	226,264	247,634
Indefinite-lived Intangible Assets [Line Items]
Accumulated amortization	$ (92,436)	(71,066)
Sponsor relationships
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life	155 months
Gross carrying amount	$ 17,200	17,200
Accumulated amortization	(4,680)	(3,705)
Net	12,520	13,495
Indefinite-lived Intangible Assets [Line Items]
Accumulated amortization	$ (4,680)	(3,705)
Technology
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life	13 months
Gross carrying amount	$ 16,470	46,952
Accumulated amortization	(14,026)	(41,335)
Net	2,444	5,617
Indefinite-lived Intangible Assets [Line Items]
Accumulated amortization	$ (14,026)	(41,335)
Trade name
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life	22 months
Gross carrying amount	$ 3,100	2,600
Accumulated amortization	(1,346)	(396)
Net	1,754	2,204
Indefinite-lived Intangible Assets [Line Items]
Accumulated amortization	$ (1,346)	(396)
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life	174 months
Gross carrying amount	$ 57,143	101,575
Accumulated amortization	(1,784)	(100,518)
Net	55,359	1,057
Indefinite-lived Intangible Assets [Line Items]
Accumulated amortization	$ (1,784)	(100,518)
CPA firm relationships
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life	174 months
Gross carrying amount	$ 4,070	0
Accumulated amortization	(136)	0
Net	3,934	0
Indefinite-lived Intangible Assets [Line Items]
Accumulated amortization	$ (136)	0
Curriculum
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life	17 months
Gross carrying amount	$ 900	1,700
Accumulated amortization	(496)	(996)
Net	404	704
Indefinite-lived Intangible Assets [Line Items]
Accumulated amortization	$ (496)	$ (996)