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Commitments and Contingencies - Additional Information (Detail) (USD $)
In Thousands, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Aug. 31, 2013
Commitments and Contingencies Disclosure [Abstract]        
Operating leases expenses $ 794us-gaap_LeaseAndRentalExpense $ 826us-gaap_LeaseAndRentalExpense    
Period in which office lease expires   Jan. 01, 2014    
New lease agreement term   16 years    
New lease agreement date   2013-08    
Lease incentives received including a deferred rent period and a leasehold improvement allowance       3,223us-gaap_LeaseIncentiveReceivable
Leasehold improvement allowance 509us-gaap_IncentiveFromLessor   509us-gaap_IncentiveFromLessor 3,223us-gaap_IncentiveFromLessor
Stand by letter of credit decreased $ 1,384wetf_LettersOfCreditDecreasedAmount