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Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017
Commitments And Contingencies [Line Items] |  |  |  |
Operating leases expenses | $ 1,289 | $ 1,030 | $ 2,316 | $ 2,150
Standby letter of credit | 1,384 |  | 1,384 |
AdvisorEngine [Member] |  |  |  |
Commitments And Contingencies [Line Items] |  |  |  |
Remaining commitment amount | $ 3,000 |  | $ 3,000 |

X
- Definition Amount of rent expense incurred for leased assets, including but not limited to, furniture and equipment, that is not directly or indirectly associated with the manufacture, sale or creation of a product or product line. + References No definition available. + Details
Name: | us-gaap_LeaseAndRentalExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The total amount of the contingent obligation under letters of credit outstanding as of the reporting date. + References No definition available. + Details
Name: | us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Commitments and contingencies. + References No definition available. + Details
Name: | wetf_CommitmentsAndContingenciesLineItems
Namespace Prefix: | wetf_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- 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

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=wetf_AdvisorEngineMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |