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

Date when the acquirer obtains control of the acquiree, in CCYY-MM-DD format.

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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of assets, excluding financial assets and goodwill, lacking physical substance and having a projected indefinite period of benefit.

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