Securities Held-to-Maturity - Additional Information (Detail) - Securities	6 Months Ended	12 Months Ended
Jun. 30, 2019	Dec. 31, 2018
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.

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