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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
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

X

- 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

X

- Definition

Notes and loans receivable aggregate commitment amount.

+ References

No definition available.

+ Details

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Namespace Prefix:	wetf_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Notes and loans receivable remaining commitment amount.

+ References

No definition available.

+ Details

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Namespace Prefix:	wetf_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: