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Goodwill and Intangible Assets - Additional Information (Detail) - USD ($) $ in Thousands | 3 Months Ended |  |
--- | --- | --- | ---
Mar. 31, 2021 | Dec. 31, 2020 | Apr. 11, 2018
Indefinite-lived Intangible Assets [Line Items] |  |  |
Goodwill | $ 85,856 | $ 85,856 |
Intangible asset related to its customary advisory agreement | $ 601,247 | $ 601,247 |
Acquisition completion date | Apr. 11, 2018 |  |
Acquisition of ETFS Business [Member] |  |  |
Indefinite-lived Intangible Assets [Line Items] |  |  |
Goodwill |  |  | $ 84,057
Intangible asset related to its customary advisory agreement | $ 601,247 |  |

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