Goodwill and Intangible Assets - Additional Information (Detail) $ in Thousands, $ in Thousands		3 Months Ended
	Apr. 11, 2018 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2017 USD ($) Fund	Dec. 31, 2017 CAD ($) Fund	Dec. 31, 2018 USD ($)
Indefinite-lived Intangible Assets [Line Items]
Intangible asset related to its customary advisory agreement		$ 603,251			$ 603,209
Questrade ETFs [Member]
Indefinite-lived Intangible Assets [Line Items]
Intangible asset related to its customary advisory agreement		2,004			1,962
Questrade ETFs [Member] | WisdomTree Asset Management Canada, Inc [Member]
Indefinite-lived Intangible Assets [Line Items]
Number of ETF acquired by company | Fund			8	8
Business acquisition, cash paid			$ 2,132	$ 2,675
Acquisition Of Etfs Business [Member]
Indefinite-lived Intangible Assets [Line Items]
Business acquisition, cash paid	$ 253,000
Intangible asset related to its customary advisory agreement		$ 601,247			$ 601,247
Weighted average cost of capital percentage	11.60%
Acquisition completion date		Apr. 11, 2018
Acquisition Of Etfs Business [Member] | Minimum [Member]
Indefinite-lived Intangible Assets [Line Items]
Revenue growth multiple	3.00%
Acquisition Of Etfs Business [Member] | Maximum [Member]
Indefinite-lived Intangible Assets [Line Items]
Revenue growth multiple	4.00%