Securities Held-to-Maturity - Additional Information (Detail) - Securities	9 Months Ended	12 Months Ended
Sep. 30, 2017	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Number of securities determined to be other than temporarily impaired	0	0

Number of securities determined to be other than temporarily impaired.

No definition available.

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Namespace Prefix:	wetf_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration