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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% |  |  |  |

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