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Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Sep. 30, 2018	Jun. 30, 2018
Commitments And Contingencies [Line Items]
Operating leases expenses	$ 1,027	$ 1,120
Standby letter of credit	1,384
AdvisorEngine [Member]
Commitments And Contingencies [Line Items]
Remaining commitment amount	$ 8,000
AdvisorEngine [Member] | Scenario, Forecast [Member]
Commitments And Contingencies [Line Items]
Remaining commitment amount			$ 3,000	$ 5,000

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:	us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=wetf_AdvisorEngineMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

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