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Variable Interest Entity - Additional Information (Detail) - AdvisorEngine [Member] - USD ($) $ in Thousands | Sep. 30, 2018 | Jun. 30, 2018 | Dec. 31, 2017 | Dec. 29, 2017
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Variable Interest Entity [Line Items] |  |  |  |
Aggregate commitment amount |  |  |  | $ 30,000
Remaining commitment amount |  |  | $ 8,000 |
Scenario, Forecast [Member] |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |
Remaining commitment amount | $ 3,000 | $ 5,000 |  |

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- Definition 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. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Notes and loans receivable aggregate commitment amount. + References No definition available. + Details
Name: | wetf_NotesAndLoansReceivableAggregateCommitmentAmount
Namespace Prefix: | wetf_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Notes and loans receivable remaining commitment amount. + References No definition available. + Details
Name: | wetf_NotesAndLoansReceivableRemainingCommitmentAmount
Namespace Prefix: | wetf_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_StatementScenarioAxis=us-gaap_ScenarioForecastMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |