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Securities Held-to-Maturity - Schedule of Securities Held-to-Maturity (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Held-to-maturity Securities [Line Items]
Federal agency debt instruments	$ 21,299	$ 22,496
Federal Agency [Member]
Schedule of Held-to-maturity Securities [Line Items]
Federal agency debt instruments	$ 21,299	$ 22,496

X

- Definition

Amount before other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

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

- Details

Name:	us-gaap_DebtSecurityAxis=wetf_FederalAgencyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: